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ATHENA OpticMin © Pierre Perroud (2016): Search common rock forming minerals from optical properties observed with the petrographic microscope
Pierre Perroud, Susanne Theodora Schmidt, Annette Süssenberger
Plates are part of the "Atlas of rock-forming minerals (transmitted light)" by Susanne Theodora Schmidt, University of Geneva, 108 p
Plagioclase calculation module by Christian de Capitani, University of Basel.
I wrote OpticMin for my own use: you may use it at your own risk. You are welcome to send corrections and suggestions.
Version: see update date at the bottom of the page
This multiple search table helps to rough out the study of exercise thin plates. Here are some of the most common rock-forming minerals. They represent about 90% of the rock forming minerals. There are more than 5000 mineral species (end 2015); if your mineral is uncommon you will not find it here. See bibliography at the bottom of the page: books and publications are irreplaceable to go deeper into your search results and ascertain them. If you use this search table, please contribute with sending corrections and comments.
Columns
Columns and data have been strongly compressed to fit page width. Columns are sortable. Data are for standard thin sections (standard thickness, fresh polished, unstained), correct illumination, etc. (see manuals in the bibliography below).
01. Mineral. Mineral name, or group, or series (According to H. Strunz).
Formula. Formula and references can be found here: Athena. Some names are redundant (e.g. mineral name and group name) to make search easier.
02. Color. Color in thin section PPL (plane polarized light). Search suggestions: colorless, blue, pinkish, etc.
Pleochroism. Search suggestions: Pl., weak, distinct, strong, color names
03. Form. Habitus. Irregular forms and grains are not mentioned.
04. Cleavage. Search suggestions: perfect, good, distinct, poor, a form symbol (e.g. {110}, etc.), //, basal, parting
05. Twinning. Search suggestions: a twinning name (e.g. Carlsbad, etc.), simple, lamellar, polysynthetic, //, a form symbol (e.g. {110}, etc.)
06. Extinction angle. Search suggestions: symmetrical, //, basal.
Elongation sign: length slow (positive elongation), length fast (negative elongation).
07. Birefringence. Δn=(ne-no) or (nz-nx). Search suggestions: 1st, 2nd, 3rd, 4th, 5th, high upper order.
08. Relief. Positive when R.I mineral is greater than the R.I. of the mounting material (~1.54). Negative when R.I. mineral is lower.
Search suggestions: H(-), M(-), L(-), L(+), M(+), H(+), VH(+). Values are from W. Nesse: H(-) <1.42; M(-) 1.42-1.50; L(-) 1.50-1.54; L(+) 1.54-1.58; M(+) 1.58-1.66, H(+) 1.66-2.00, VH(+) > 2.00 .
R.I.: Refractive Indices. isotropic: n; uniaxial: ne, no (=nε, nω); biaxial: nx, ny, nz (= nα, nβ, nγ). You should verify; they are not exactly the same from one book to another. You can try with rough data: 1.5, 1.6, etc.
09. Indicatrix (Interference figure and optical sign). Conoscopy. Search suggestions isotropic, U(+), U(-), B(+), B(-).
System. Search suggestions: cubic, tetragonal, trigonal, hexagonal, orthorhombic, monoclinic, triclinic.
10. 2V angle: B+ when 2Vz (=2Vγ) is acute; B- when 2Vx (=2Vα ) is acute. 2V examples.
Dispersion. Search suggestions: r>v, r<v, weak, moderate, strong
11. Occurrence. Paragenesis. Alteration. This column is obviously very incomplete.1. Use a large screen, high-definition.
2. Read explanations above.
3. Choose the number of results you wish to display per page.
4. Enter your query (anything: name, color, form, etc.). You can use truncated words (e.g. 'twin' will find 'twins', 'twinning', etc.). Avoid using numbers (Δn, R.I., 2V, etc.): you cannot search within a range.
5. Refine search . You can refine the refined search. Etc.!
6. Refresh (reload) the page for new search.
| Mineral name. Formula | Color PPL. Pleochroism | Form. Habitus | Cleavage | Twinning | Extinction. Elongation | Birefringence | Relief. R.I.(± 0.002) | Indicatrix. System | 2V angle. Dispersion | Occurrence. Paragenesis. Alteration |
|---|
| Mineral,Formula | Color ppl,Pleochroism | Form,Habitus | Cleavage | Twinning | Extinction,Elongation | Birefringence | Relief,R.I.(± 0.002) | Indicatrix,System | 2V,Dispersion | Occurrence,Paragenesis,Alteration |
|---|---|---|---|---|---|---|---|---|---|---|
| ACTINOLITE []Ca2(Mg,Fe++)5Si8O22(OH)2 (Inosilicate. Clinoamphibole, Tremolite - Actinolite - Ferro-actinolite series.)  | Pale yellow green, blue green to dark green. Color increases with Fe content. Pl. X= colorless, pale yellow green, Y= pale yellow green, pale blue green, green Z= pale green, green, blue-green, dark green | Prismatic, columnar, bladed, acicular, fibrous. Rhombic basal section. | {110} intersects at 56° and 124°. Visible on basal sections. Parting on {100} and {010} (rare) | Simple or {100} lamellar, // to the long diagonal of the basal section | Inclined ext. 10°-17° Sections // to (100) show // extinction Length slow. | Δn=0.017-0.022 Upper 1st order to mid 2nd order. | M(+) to H(+) nx=1.620-1.670 ny=1.630-1.675 nz= 1.645-1.688 R.I. increases with increasing Fe content. | B(-) Monoclinic | 2Vx=74°-84° r<v weak | Low grade metamorphic rocks. Meta-basalts, meta-gabbros, with chlorite. With calcite, dolomite, forsterite, garnet, diopside, wollastonite, talc, epidote. Also in metamorphic mafic, ultramafic rocks. In blue schists. Altered to chlorite, talc, carbonates. |
| AEGIRINE NaFe+++Si2O6 (Inosilicate, sodic clinopyroxene; sometimes named acmite) | Bright green to yellow green. Pl. X= emerald green, deep green, Y= grass green, yellowish green, yellow, Z= brownish green, green, yellowish brown, yellow. | Stubby prismatic, elongated columnar xls | Intersects 87° in (110) Parting {001} and {100} Octagonal sections show 87° cleavages. | Simple and lamellar on {100} | Inclined ext. 0°-10° in (010) Basal section: symmetrical ext. (110) | Δn=0.045-0.060 3rd order | H(+) nx=1.750-1.776 ny=1.780-1.820 nz=1.795-1.836 | B(-) Monoclinic | 2Vx=60°-70° r>v moderate to strong | In alkaline igneous rocks: alkali granite, syenite, nepheline syenite. In carbonatites, glaucophane schists. Altered to amphibole (uralite), chlorite |
| AEGIRINE-AUGITE (Ca,Na)(Mg,Fe++,Fe+++)Si2O6 (Inosilicate, sodic-calcic clinopyroxene) | Pale green to yellow green. Pl. X= bright green, deep green, brownish green, Y= yellowish green, Z=yellow, greenish brown, brownish green. Color zoning, dark rim. | Stubby prismatic, elongated xls. Octagonal sections show 87° cleavages. | Intersects 87° in (110) Parting {001} and {100} | Simple and lamellar on {100} | Inclined ext.: 0°-20° in (010) Basal section: symmetrical ext. (110) | Δn=0.030-0.053 2nd order to lower 3rd order | H(+) nx=1.700-1.760 ny=1.710-1.800 nz=1.730-1.813 | B(-) or B(+) Monoclinic | 2Vx=70°-110° r>v moderate to strong | In alkalic igneous rocks with sodic amphiboles, K-feldspars and nepheline: alkali granite, quartz syenite, nepheline syenite. In sodic volcanic rocks: peralkaline rhyolites In carbonatites, glaucophane schists. Altered to amphibole (uralite), chlorite |
| AENIGMATITE Na2Fe++5Ti++++Si6O20 (Inosilicate, aenigmatite - sapphirine - surinamite group) | Dark reddish brown, nearly opaque Pl. X= light yellow brown, reddish brown, Y= reddish to dark chestnut brown, Z= deep reddish brown, brownish black, opaque | Long prismatic xls. | {100} and {010} perfect | {1-10} polysynthetic twins | Inclined ext. | Δn=0.07 Very high upper orders, 4th order | (H+) nx=1.81 ny=1.82 nz=1.88 | B(+) Triclinic | 2Vz=32° (27°-55°) | In Si-poor lava. In Na-rich magmatic rocks. Alkaline rhyolite, trachyte, phonolite. In nepheline and sodalite syenites. With aegirine-augite, arfvedsonite or riebeckite, anorthoclase and nepheline. Homoaxial intergrowth with arfvedsonite is common; |
| ALBITE, high NaAlSi3O8 (Tectosilicate, plagioclase, An0-An10) | Colorless | Prismatic elongated laths in magmatic rocks, bladed. Anhedral in metamorphic rocks. | {001} perfect, {010} good, {110} poor | Non-twinned, simple and polysynthetic albite twins (010) Pericline (h01) polysynthetic. Carlsbad penetration. | Inclined. Michel-Lévy method or Carlsbad-Albite method Calculate with Ch. de Capitani | Δn=0.007-0.008. 1st order grey or white. Optic related to anorthite content | L(-) to L(+) nx=1.526-1527 ny=1.532-1.533 nz=1.534-1.541 Difficult to distinguish. | B(-) Triclinic | 2Vx=50°-54° r>v weak | High temperature lavas. Altered to kaolin, sericite |
| ALBITE, low NaAlSi3O8 (Tectosilicate, plagioclase, An0-An10) | Colorless, clouded (alteration) Perthite: albite exsolutions in microcline or orthoclase | Tabular, // to (010), prismatic, elongated. Common chemical zoning. | {001} perfect, {010} good, {110} poor | Non-twinned, simple and polysynthetic albite twins (010). Pericline (h01) polysynthetic. Carlsbad penetration. | Inclined. Michel-Lévy method or Carlsbad-Albite method Calculate with Ch. de Capitani | Δn=0.011. 1st order grey or white. Optic related to anorthite content | L(-) nx=1.527 ny=1.531 nz=1.538 Difficult to distinguish | B(+) Triclinic | 2Vx=77°-84° v>r weak | In plutonic rocks, granite, granodiorite, pegmatites, syenite. Hydrothermal veins (pericline). Volcanic: rhyolite. Low grade pelitic metamorphic Altered to calcite, sericite, zeolites, muscovite, kaolinite, prehnite, pyrophyllite, epidote (saussurite) |
| ALUNITE K2Al6(SO4)4(OH)12 (Sulfate) | Colorless | Tabular, square section, rhombic section, flaky, granular | {001} | Ext. // to cleav. {001} Length fast | Δn=0.010-0.023 Increases with Fe | M(+) no=1.572-1.620 ne=1592-1.641 | U(+) Hexagonal | In altered volcanic rocks: Hydrothermal alteration of feldspars. | ||
AMPHIBOLE | Green, brown, colorless or blue). Typically paler amphiboles contain less Fe and more Mg. Pleochroic. Glaucophane (blue-mauve, colorless). Actinolite (colorless - blue green - green). Tremolite (colorless). Hornblende (green brown). | Amphibole forms typically well-shaped crystals in rocks with abundant quartz or plagioclase. Ideal crystal forms are prismatic elongated with rhombic-shaped or stretched hexagon cross section. In rocks with abundant Fe-Mg silicates amphibole typically is equant. | Cross sections show two cleavages intersecting at ~120°. (56° and 124°) in {110} | Inclined extinction (typically <30°) Symmetric: basal section. Parallel (100) | Δn=0.01-0.03 1st order to upper 2nd order | M(+) H(+) From nx ~ 1.6 to nz ~ 1.8 | B(+) or B(-) Orthorhombic Monoclinic | 2V=very variable, 35° - 130° | Plutonic, volcanic, metamorphic. Brown hornblende (basalt). Green hornblende (diorite, granite). Glaucophane (metabasalt, metagabbro). Actinolite rims around metamorphosed pyroxenes. Glaucophane - Na-rich stable at low T and high P (blue schists). Tremolite - Mg-rich found in metamorphosed carbonates and peridotites. Actinolite – Fe-rich stable at moderate T in metamorphic rocks. Hornblende – Fe-Al-rich stable at high T in igneous rocks and high T in metamorphic rocks Altered to: Chlorite (pale green). Commonly replaces: Clinopyroxene . Distinguishing features: Biotite (one cleavage, // extinction; bird's eye polarization). Chlorite (green, low and anormal interference colors). Pyroxene (two cleavages at 90°, higher extinction angle, typically paler colored). | |
| ANALCIME Na[AlSi2O6].H2O (Tectosilicate, zeolite, analcime group) (analcite: not IMA name) | Colorless | Trapezohedrons. 8 sided sections, anhedral. | {001} very poor | {001}, {110}, lamellar | Isotropic. Δn=0.001. Very weak. Lower 1st order | M(-) n=1.479-1.493 | Isotropic Cubic | In Si-deficient igneous rocks: syenite,Hydrothermal alteration of basalt Altered to pseudoleucite, zeolites | ||
| ANDALUSITE Al2SiO5 (Nesosilicate sillimanite - andalusite - kyanite group) | Colorless. Rarely pink or greenish with weak pleochroism. Pl. X= pink, Y=Z= greenish yellow, colorless. Colors uneven distributed. Color darker when Mn or Fe increase. | Prismatic with square section. Cross dark inclusions in chiastolite formed by sericite and/or opaques minerals. | 2 good {110} cleavages nearly at right angle. Rarely visible. | Twinning {101} rare | // extinction Symmetric extinction in basal sections. Length fast | Δn=0.009-0.013. Often 1st order grey, white, yellow. | M(+) nx=1.629-1.640 ny=1.634-1.644 nz=1.638-1.650 | Orthorhombic B(-) | 2Vx=71°-88° r<v weak; rarely r>v | Contact and regional metamorphic rocks: hornfels, mica schist. Also in granite, pegmatite With cordierite, staurolite, garnet, sillimanite, kyanite, chlorite, muscovite, plagioclase. Altered to sericite, chlorite |
| ANDESINE (Na,Ca)[Al(Si,Al)Si2O8] (Tectosilicate, plagioclase, An30-An50) | Colorless, clouded (alteration) | Tabular, // to (010), prismatic elongated. Common chemical zoning in magmatic rocks. Anhedral in metamorphic rocks. | {001} perfect, {010} good, {110} poor | Non-twinned, simple and polysynthetic albite twins (010). Pericline (h01) polysynthetic. Carlsbad penetration. | Inclined. Michel-Lévy method or Carlsbad-Albite method Calculate with Ch. de Capitani | Δn=0.008. Low: 1st order up to grey Optic related to anorthite content | L(+) An40: nx=1.549 ny=1.553 nz=1.557 | B(+) Triclinic B(+) plutonic rocks B(-) volcanic rocks | 2Vx=83° r>v weak 2V=78°-90° in plutonic rocks 2V=80°-100° in volcanic rocks | In felsic and intermediate igneous rocks Volcanic: andesite. Metamorphic medium and high grade. Altered to calcite, sericite, zeolites, muscovite, kaolinite, scapolite, prehnite, pyrophyllite |
| ANHYDRITE CaSO4 (Sulfate) | Colorless Rare weak violet Pl. | Prismatic, tabular, fibrous, radiating | 3 pinacoidal cleavages at right angle: {010} perfect, {100} good, {001} good | Simple on {011} | Ext. // cleavages and xl faces. Acicular xls: // extinction. Length slow if elongate on c | Δn=0.040-0.044 Vivid 2nd order colors | M(+) nx=1.569-1.574 ny=1.574-1.579 nz=1.609-1.618 | Orthorhombic B(+) | 2Vz=42°-44° r<v distinct | In evaporites, with halite, sylvite, calcite, dolomite, gypsum, clay. Hydrothermal. Volcanic amygdules Altered to gypsum |
| ANKERITE Ca(Fe++,Mg,Mn)(CO3)2 (Carbonate. Dolomite group) | Colorless, brownish (if iron oxides) | Rhombohedral, also curved faces | {10-11} perfect | {02-21} lamellar Simple: {0001}, {10-10}, {11-20}, {10-11} | Symmetrical or inclined | Δn=0.182-0.202 High upper order white or grey | L(-) L(+) M(+) H(+) no=1.690-1.750 ne=1.510-1548 | U(-) Hexagonal, Trigonal | In veins in Fe sediments with siderite and Fe-oxides. In schists with amphibole. | |
| ANORTHITE CaAl2Si2O8 (Tectosilicate, plagioclase, An90-An100) | Colorless, clouded (alteration) | Tabular, // to (010), prismatic elongated. Common chemical zoning. | {001} perfect, {010} good, {110} poor | Simple and polysynthetic (010). Polysynthetic pericline. Carlsbad penetration | Inclined. Michel-Lévy method or Carlsbad-Albite method Calculate with Ch. de Capitani | Δn=0.013. 1st order grey or white, up to yellow. Optic related to anorthite content | L(+) An100: nx=1.577 ny=1.585 nz=1.590 R.I. decreases with Ab content. | B(-) Triclinic | 2Vx=75°-80° v>r weak | Mafic rocks. Volcanic: basalt Rare in metamorphic carbonate rock Altered to calcite, sericite, zeolites, muscovite, paragonite, kaolinite, scapolite, prehnite, pyrophyllite |
| ANORTHOCLASE (Na,K)AlSi3O8 (Tectosilicate, K feldspar, Ab63-Ab90) | Colorless | Prismatic xls | {001} perfect, {010} distinct intersect at ~92° | Complex twinning according to albite and pericline laws. Polysynthetic on {010} Ultra-fine cross-hatched twinning.. | Inclined ext. 4°-10° on {001} cleavage | Δn=0.006-0.007 1st order grey or white. | L(-) nx=1.524-1.526 ny=1.529-1.5342 nz=1.530-534 R.I. increases with Na content. | B(-) Triclinic | 2Vx=42°-52° r>v weak | In high temperature Na rich volcanic. rocks rhyolite, trachyte, phonolite. Altered to kaolinite, sericite, cryptocrystalline silica |
| ANTHOPHYLLITE []Mg7Si8O22(OH)2 (orthoamphibole) | Colorless, pale brown. Darker with higher Fe content. Weak Pl. X= colorless, pale yellow, pale grey brown, pale greenish yellow, Y= colorless, pale grey brown, pale greenish yellow, Z= pale grey brown, purplish brown, grey green. | Prismatic columnar, bladed, acicular. Rhombic basal section | {210} perfect, prismatic cleavages intersect at 55°-125° | Symmetrical (basal). // (longitudinal) ext. on {110} cleavage Length slow. | Δn=0.013-0.028 1st order red (B+), 2nd order blue (B-). | M(+) to H(+) nx=1.587-1.668 ny=1.602-1.670 nz=1.613-1.680 R.I. increases with increasing Fe content. | B(+) or B(-) High Mg are B(-) Orthorhombic | 2Vx=65°-122° Moderate, r<v (+), r>v (-) | Medium and high grade metamorphic: amphibolite, gneiss, granulite, hornfels, talc schist. With garnet, cordierite, hornblende, sillimanite, plagioclase. Altered to serpentine, talc at low temperatures | |
APATITE | Colorless (except for strong colored specimens). Weak to moderate pleochroism, e>o. | Prismatic, elongated xls, hexagonal cross section. | Poor {001} | Rare | // extinction Length fast | Δn=0.001-0.007. 1st order grey. Carbonate-apatite: up to lower 2nd order | M(+) no=1.629-1.667 ne=1.624-1.666 | U(-) Hexagonal B(-) with 2v<10° | Igneous and metamorphic. In phosphatic limestone, shale, phosphate deposits. Hydrothermal. | |
| ARAGONITE CaCO3 (Carbonate) | Colorless | Prismatic, // or radiated aggregates | {010} imperfect | {110} produces pseudohexagonal form | Ext. // Length fast | Δn=0.155 High upper order white | L(-) L(+) M(+) H(+) nx=1.530 ny=1.680 nz=1.685 | B(-) Orthorhombic | 2Vx=18° (up to 23° with increasing Pb) v>r weak | Sedimentary. In hot springs. Volcanic, in basalt, andesine, with zeolites Metamorphic. In high pressure low temperature blue schist with glaucophane, crossite, lawsonite, In aegirine-albite rocks. In serpentine with dolomite, magnesite, brucite. |
| ARFVEDSONITE NaNa2(Fe++,Mg)4Fe+++Si8O22(OH)2 (Inosilicate, clinoamphibole. Series arfvedsonite - eckermannite) | Blue green, brown, violet to almost opaque. Absorption colors form deep Prussian blue to brownish green. Anomalous interference colors due to strong absorption. Pl. X= blue green, Y= light blue green, brown yellow, grey violet, Z= yellow green, blue grey, brownish green, black | Bladed, prismatic, fibrous. Rhombic basal section. | {110} intersects at 56° and 124°. Parting on {010} | Simple or lamellar on {100} | Symmetrical (basal). // (100). Inclined on other longitudinal sections Length fast. | Δn=0.005-0.012 Low, up to mid 1st order. Basal sections show low order. | H(+) nx=1.62-1.70 ny=1.63-1.71 nz=1.64-1.71 | B(+) or B(-) Monoclinic | 2Vx=0°-100° | In alkaline igneous rocks and peralkaline volcanic rocks: alkali granite, syenite, trachyte, phonolite, pegmatite. With aegirine, aegirine-augite, biotite, feldspar, nepheline. Altered to amphibole (uralite), iron oxides, chlorite. |
| ARMENITE BaCa2Al6Si9O30.2H2O (Cyclosilicate. Milarite group) | Colorless | Prismatic | Perfect prismatic. Distinct pinacoidal | Complex showing triplets. Also lamellar. Partings along sector boundaries | Δn=0.009-0.011 | L(+) nx=1.550-1.551 ny=1.557-1.559 nz=1.559-1.562 | B(-) with U(-) domains Orthorhombic, pseudohexagonal | 2Vx=60°-65° | Associations: with axinite, pyrrhotite, quartz in calcite veins; albite, with Mn zoisite, piemontite, prehnite, epidote, muscovite in Mn metasomatized diorite; with celsian, margarite, quartz, zoisite, ganterite in gneiss | |
| AUGITE (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6 (Inosilicate, calcic clinopyroxene) | Colorless, grey, pale green, pale brown, brownish green. Titanaugite: purplish, brown, brown-violet. Color zoning: concentric, hourglass pattern. No or weak Pl. X= pale green, bluish green, Y= pale greenish brown, green, bluish green, Z= pale brownish green, green, yellow green | Stubby prismatic xls. Basal section: 4 or 8 sided. | {110} distinct, intersect at ~87°. Parting {001} and {100} | {100} or {001} lamellar, both combined as herringbone pattern | Basal (2 cleavages) symmetrical ext. // c: inclined 35°-48° on {110} cleavage // (100) is length slow | Δn=0.018-0.034 Up to mid 2nd order. Exsolved orthopyroxene lamellae. | H(+) nx=1.671-1.735 ny=1.672-1.741 nz=1.703-1.761 R.I. increases with Fe content | B(+) Monoclinic | 2Vz=25°-70° increase with Ca content r>v weak r<v strong in Ti augite | Plutonic, volcanic and high grade meta-igneous Igneous: gabbro, granodiorite, ultramafic, mafic. Volcanic: basalt, andesite. Metamorphic: amphibolite, gneiss, skarn. With tremolite-actinolite, grossular, epidote, wollastonite, forsterite, monticellite, calcite, dolomite. Altered to hornblende, amphibole (uralite), serpentine, chlorite, epidote, carbonates. |
| AZURITE Cu3(CO3)2(OH)2 (Carbonate) | Blue. Weak Pl. X=clear blue, Y=Azure blue, Z=dark blue, violet blue | Tabular, radiated | {011} perfect, {100} fair, {110} poor | Rare. {-101}, {-102}, {001} | Length slow | Δn=0.106 High order cream white masked by mineral color | H(+) nx=1.730 ny=1.756 nz=1.836 | B(+) Monoclinic | 2Vz=68° | In oxidized zone of hydrothermal Cu deposits Replaced by malachite. |
| BARROISITE []{CaNa}{Mg3Al2}(AlSi7O22)(OH)2 (Inosilicate) | Monoclinic | |||||||||
| BARYTE BaSO4 (Sulfate) | Colorless. Weak Pl., pale colors | Tabular, prismatic | {210} 2 very good, intersects at 78° {010} good Basal {001} intersects 3 others at 90° | {110} | // Length slow Basal: symmetrical ext. | Δn=0.012 | M(+) nx=1.634-1.637 ny=1.636-1.639 nz=1.646-1.649 | B(+) Orthorhombic | 2Vz=36°-40° r<v | In hydrothermal veins. Sedimentary rocks. Altered to witherite |
| BERYL Be3Al2Si6O18 (Cyclosilicate) | Colorless Colored varieties with Pl. o<e o= light blue, e= blue or o= yellowish green, e= green | Elongated prismatic hexagonal. Basal sections: hexagonal. Longitudinal sections: rectangular | {001} poor | Rare | // ext. Length fast | Δn=0.004-0.009 | L(+) M(+) no=1.569-1.610 ne=1.560-1.599 | U(-) Hexagonal | In granitic pegmatites with quartz, K-Feldspar, albite, muscovite, biotite, tourmaline. In granite, In nepheline syenite. High temperature hydrothermal with Sn and W minerals. Altered to sericite, clay | |
| BIOTITE K(Mg,Fe++)3(Al,Fe+++)Si3O10(OH,F)2 (Phyllosilicate. A series name in the mica group) | Brown, brownish green, reddish brown. Mottled interference colors Phlogopite is pale brown, colorless. Pleochroic halos around radioactive minerals Strong Pl. X= colorless, pale yellow, light brown, greenish brown, pale green, Y=Z= brown, olive brown, dark green, dark red brown | Tabular, lamellar, bladed, hexagonal section. Bent during deformation. | {001} perfect, thin | Rare | Ext . //, rarely inclined up to max. ~9° Length slow: Wave extinction on bent grains. (Amphiboles: inclined ext.) | Δn=0.028-0.07 Strong, 2nd order, 3rd order, 4th order. Pebbly, birds-eye texture seen near extinction | L(-) L(+) M(+) H(+) nx=1.530-1.625 ny=1.557-1.696 nz=1.558-1.696 R.I. increases with Fe content. | B(-) Monoclinic | 2Vx=0°-25° Lepidolite: smaller 2V r<v weak (r>v Mg rich varieties) | Igneous rocks. Metamorphic rocks, phyllite, schist, gneiss, hornfels. Phlogopite in ultramafic rocks, in metamorphosed carbonates Altered to chlorite, vermiculite, calcite, Fe-Ti oxides |
| BRONZITE (En88-En70) (Mg,Fe++)2Si2O6 (Inosilicate, orthopyroxene, Enstatite - Ferrosilite series) (A ferroan enstatite) | Pale colored. Pl. X= pink, brownish pink, pale yellow, Y= light brown, yellow, pinkish yellow, greenish yellow, Z= light green, grey green, bluish green | Stubby prismatic. Basal sections 6 or 8 sides, showing cleavages Exsolution lamellae (augite) | Good // {210}, intersect at ~ 88°. Exsolution lamellae (augite) Parting on {010} and {001}. | Fine lamellar // {100} is often exsolution lamellae | Ext. // Basal: symmetrical Cleavage trace length slow | Δn=0.011 1st order | H(+) En80: nx=1.677 ny=1.685 nz=1.690 | B(-) Orthorhombic | 2Vz=50°-90° r>v moderate | In charnockite, with diopside and hornblende. |
| BRUCITE Mg(OH)2 (Hydroxide) | Colorless | Foliated, fibrous, flakes | {001} perfect | Ext. // Length fast | Δn=0.010-0.021 Strong dispersion. Anomalous 1st order red brown or blue | M(+) no=1.560-1.590 ne=1.580-1.600 | U(+) Hexagonal, Trigonal | From alteration of periclase in marble In serpentinite and chlorite schist, with talc, magnesite Altered to hydromagnesite | ||
| BYTOWNITE (Ca,Na)[Al(Al,Si)Si2O8] (Tectosilicate, plagioclase, An70-An90) | Colorless, clouded (alteration) | Tabular, // to (010), prismatic elongated. Common chemical zoning. | {001} perfect, {010} good, {110} poor | Albite polysynthetic. Pericline polysynthetic. Carlsbad penetration | Inclined. Michel-Lévy method or Carlsbad-Albite method Calculate with Ch. de Capitani | Δn=0.010. 1st order grey or white, up to yellow Optic related to anorthite content | L(+) An80: nx=1.569 ny=1.574 nz=1.579 | B(+) or B(-) Triclinic | 2Vx=87°-103° v>r weak | In gabbro, anorthosite, mafic rocks. In stony meteorites. Altered to calcite, sericite, zeolites, muscovite, paragonite, kaolinite, scapolite, prehnite, pyrophyllite |
| CALCITE CaCO3 (Carbonate, calcite group) | Colorless, cloudy Iridescence along cleavages. Relief Pl. | Scalenohedrons, rhombohedrons, prismatic, spherulitic, etc. | {10-11} perfect, . Intersects at 74°57'. {01-12} parting Some deformation twins (if present) bisect acute cleavage angle. (see dolomite) | {01-12} lamellar {0001} contact | Extinction: inclined or symmetrical to cleavage faces. Length slow | Δn=0.172 High upper order grey | M(-) L(-) M(+) H(+) no=1.658 ne=1.486 | U(-) Hexagonal, Trigonal | Ubiquitous. Sedimentary. Metamorphic, marble, with wollastonite, garnet, olivine, diopside, vesuvianite, tremolite, epidote. In igneous rocks with nepheline, feldspathoids. Hydrothermal. Altered to dolomite, replaced by quartz, opal, Fe or Mn oxides | |
| CANCRINITE Na6Ca2Al6Si6O24(CO3)2 (Tectosilicate, cancrinite group) | Colorless | Hexagonal prisms | Perfect prismatic {100} 3 directions 60°, perfect {001} poor | // ext. Length fast (Microsommite is length slow) | Δn=0.002-0.025 Δn decrease as Na - SO4 replaces Ca - CO3 | L(-) M(-) no=1.490-1.528 ne=1.488-1.503 R.I. decrease as Na - SO4 replaces Ca - CO3 | U(-) Hexagonal Microsommite is U(+) | In nepheline syenite. With nepheline, calcite,sodalite, K-feldspars, melanite, wollastonite, corundum, K-pyroxenes, amphiboles. Vishnevite contains Na and SO4. Replaced by calcite. | ||
| CELADONITE K(Mg,Fe++)Fe+++(Si4O10)(OH)2 (Phyllosilicate, mica group) | X = pale yellow green, Y=Z = dark green, blue green | Scales | Perfect {001} | Δn=0.014 to 0.032 | nx=1.606-1.610 ny=1.610-1641 nz=1.610-1.641 | B(-) Monoclinic | 2Vz=0° to 20° | Altered volcanic rocks | ||
| CELESTINE SrSO4 (Sulfate) | Colorless, pale blue, pale blue-green, pale violet Weak Pl. blue, lavender, blue green, violet shades | Prismatic, elongated, tabular | {001} perfect 2 good prismatic {210} intersect at 75° {010} poor | // ext on c and // to {210} cleavages Length fast on c. | Δn=0.009-0.010 1st order grey, white, pale yellow ~0.002 birefringence on (100) section | M(+) nx=1.621-1.622 ny=1.623-1.624 nz=1.630-1.632 | B(+) Orthorhombic | 2Vz=51° r<v | Sedimentary. Evaporites, with gypsum, anhydrite, halite. In limestone. Hydrothermal | |
| CELSIAN BaAl2Si2O8 (Tectosilicate, Ba feldspar) | Colorless | Tabular, prismatic, elongated xls. | {001} perfect, {010} distinct, intersecting at 90°. {110} poor | Simple, Carlsbad, Manebach, Baveno. No multiple twinning. | Inclined ext. max. 29° to {001} cleavage | Δn=0.009-0.013 1st order grey, white or yellow. | M(+) nx=1.579-1.587 ny=1.583-1.593 nz=1.588-1.600 | B(+) Monoclinic | 2Vz=83°-90° | Hydrothermal veins in rich Mn rocks. Granite gneiss. With Mn minerals, rhodonite, rhodochrosite, spessartine |
| CHABAZITE (Tectosilicate, zeolite, chabazite - levyne group) (A series name: Chabazite-Ca, -K, -Mg, -Na, -Sr) | Colorless | Rhombohedral with 93°-94° angles, ~ like cubes | 3 good cleavages on {101} | Penetration and lamellar twins | Δn=0.002-0.010 1st order grey | L(-) M(-) no=1.478-1487 ne=1.480-1.493 | U(+) U(-) B(+) B(-) Triclinic, pseudohexagonal | 2V=0°-32° | In lacustrine sediments. In basalt, gabbro, serpentinite. In volcanic altered rocks Altered to clay, zeolites. | |
| CHALCEDONY SiO2 (Oxide, Quartz group, a fibrous quartz variety) | Colorless, pale brown Cloudy, nearly opaque due to inclusions. Zoning. | Spherulitic, fibrous | None. Feactures parallel to the fibers | Length fast | Δn=0.005-0.009 1st order | L(-) L(+) no=1.53-1.544 ne=1.53-1.553 | U(+) Hexagonal Trigonal Almost impossible to obtain. | Sedimentary. Volcanic. Hydrothermal. | ||
| CHLORITE (Mg,Al,Fe)3(Si,Al)4O10(OH)2.(Mg,Al,Fe)3(OH)6 (Phyllosilicate of the chlorite series: Clinochlore (Mg), Chamosite (Fe) Pennantite (Mn), etc.) | Green. Darker when more Fe. Pl. (for B+): X=Y= green, pale green, brownish green, Z= colorless, pale green, pale yellowish green Pl. (for B-): X= colorless, pale green, pale yellow green, Y=Z= pale green, green, olive green | Plates, scales, hexagonal xls | {001} perfect | Twin on (001) difficult to recognize | Ext. // to inclined ~ <9° Length fast B(+) Length slow B(-) | Δn=0.0-0.02 Often low, to 1st order white or yellow Anomalous yellow-brown, olive brown, indgo-violet | L(+) M(+) H(+) nx=1.57-1.67 ny=1.57-1.69 nz=1.57-1.69 | B(+) or B(-) Monoclinic and Triclinic | 2Vz=0°-60° (+) 2Vx=0°-40° (-) | Metamorphic. With biotite, garnet, staurolite, muscovite, andalusite, chloritoid, cordierite. Mafic. With talc serpentine, actinolite, hornblende, epidote, garnet, chloritoid. From hydrothermal alteration of biotite, amphibole, pyroxene |
| CHLORITOID (Fe++,Mg,Mn)2Al4Si2O10(OH)4 (Nesosilicate) | Green, brown, colorless. Color zoning, hourglass. Pl. X= green, grey green, Y= blue grey, reddish blue, blue green, Z= colorless, yellow, pale green | Platy, rectangular xls; hexagonal section, prismatic. Inclusions (quartz,etc.) | // {001} perfect 2 poor cleavages on {110} | Simple or lamellar on {001} | Inclined ext. 0°-18° Length fast | Δn=0.005-0.022 (often 0.010-0.012). Up to pale 1st order yellow. Varieties to lower 2nd order. | H(+) nx=1.705-1.730 ny=1.708-1.734 nz=1.712-1.740 | B(+) Monoclinic B(-) Triclinic | 2Vz=36°-72° (monoclinic) 2Vx=55°-88° (triclinic) r>v strong | Metamorphic: phyllite, quartzite, schist. In emery deposits. With garnet, staurolite, chlorite, muscovite. Altered to chlorite, sericite, clay |
| CHONDRODITE (Mg,Fe++)5(SiO4)2(F,OH)2 (Nesosilicate, humite group) | Colorless, pale yellow, yellow, orangish yellow. Darker color when Fe, Ti increase Weak Pl. X= colorless, very pale yellow, brownish yellow, Y= colorless, yellowish green, Z= colorless, pale green | Grains. Platy xls | {100} | Simple or multiple twins | Ext. in (010): 22° - 31° Length fast or length slow | Δn=0.028-0.034 2nd order | M(+) H(+) nx=1.592-1.617 ny=1.602-1.635 nz=1.621-1.646 | B(+) Monoclinic | 2Vz=50°-85° r>v | In contact metamorphic limestone and dolomite. In skarns. With tremolite, wollastonite, grossular, monticellite, forsterite, calcite, dolomite In mafic igneous rocks Altered to serpentine, chlorite |
| CLINOHUMITE (Mg,Fe++)9(SiO4)4(F,OH)2 (Nesosilicate, humite group) | Colorless, pale yellow, yellow, orangish yellow. Darker color when Fe, Ti increase Weak Pl. X= golden yellow, deep reddish yellow, Y= pale yellow, orange yellow, pale yellowish red, Z= pale yellow, orange yellow, colorless | Grains. Platy xls | {100} | Simple or multiple twins | Ext. in (010): 9°-15° Length fast or length slow | Δn=0.028-0.041 Bright upper 2nd order | M(+) H(+) nx=1.628-1.638 ny=1.641-1.654 nz=1.662-1.674 | B(+) Monoclinic | 2Vz=73°-76° r>v | In contact metamorphic limestone and dolomite. In skarns. With tremolite, wollastonite, grossular, monticellite, forsterite, calcite, dolomite In mafic igneous rocks Altered to serpentine, chlorite |
| CLINOPYROXENE (Inosilicate. A series in the Pyroxene supergroup: Augite, Clinoenstatite, Diopside, Esseneite, Hedenbergite, Jadeite, Johannsenite, Omphacite, Pigeonite, Spodumene, etc.) Fe,Mg cpx: Clinoenstatite, Pigeonite, Clinoferrosilite Ca cpx: Diopside, Hedenbergite, Augite Na,Ca cpx: Omphacite, Aegirine-Augite Na cpx: Jadeite, Aegirine Li cpx: Spodumene | Usually colorless, grey, pale green or pale brown, darker colors associated with Fe-rich varieties Titanaugite is more distinctly colored from brown/pink to violet. | Stubby prismatic elongated along the c-axis. Equant xls shapes: basal sections are 4 or 8 sided and show two cleavages at ~90° | Typical pyroxene cleavages parallel to {110}, which intersect at ~90° (87°-93°) | Simple and lamellar twins and composition planes, which in combination may form a herringbone pattern | Inclined extinction. Sections // to (010) show max. Birefringence, a single cleavage and z^c of 35 to 48° | Δn=0.018-0.034 Lower to middle 2nd order | H(+) nx=1.664-1.745 ny=1.672-1.753 nz=1.694-1.771 | B(+) B(-) Often positive Monoclinic | 2V=25°-70° | Common in mafic igneous rocks, alkali-rich varieties may be found in more silicic rocks, often associated with olivine, orthopyroxene, and plagioclase. Commonly altered to uralite (a light colored amphibole), or may alter to serpentine, chlorite, biotite, carbonates and/or other silicates. (Distinguishing features: Inclined extinction, higher birefringence, 2nd order interference colors, low 2V, optically positive in comparison with orthopyroxene Olivine lacks cleavage and has higher birefringence) |
| CLINOZOISITE Ca2Al3[Si2O7][SiO4]O(OH) (Sorosilicate. Clinozoisite - Epidote series) | Colorless. XPL: anomalous blue. interference colors unevenly distributed. No Pl. | Prismatic, columnar, bladed. Radiated. Sections rectangular or 6 sided. | {001 perfect} | Lamellar {100} | Inclined ext. 0°-30°; up to 60° Length slow | Δn=0.004-0.015Lower to middle 1st order (also anomalously bluish or greenish yellow) | H(+) nx=1.703-1.715 ny=1.707-1.725 nz=1.709-1.734 | B(+); also B(-) Monoclinic | 2Vz=14°-100° r<v clinozoisite | Green schists. Blue schists. In quartzite, slate, phyllite, chlorite schist, mica schist, gneiss, skarn, hornfels. |
| CORDIERITE Mg2Al4Si5O18 (Cyclosilicate) | Colorless. Also light blue Pl. X= colorless, pale yellow, pale green, Y= pale blue, violet, Z= pale blue | Grains. Hexagonal prismatic. | {010} | Lamellar and cyclic twinning {110}, {130} | Inclined ext. from // to 30° or 60° | Δn=0.008-0.018 1st order grey to white | L(-) L(+) nx=1.527-1.560 ny=1.532-1.574 nz=1.537-1.578 | B(-) or B(+) Orthorhombic (pseudohexagonal) | 2Vx=35°-90° (-) 2Vz=74°-90° (+) r<v weak; also r>v | In metapelites with chlorite, kyanite, andalusite, sillimanite, staurolite, muscovite, biotite, chloritoid In metamorphic with anthophyllite, garnet Altered to pinite, a mixture of mica and clay minerals. |
| CORUNDUM Al2O3 (Oxide) | Colorless, pale blue, red. Irregular patches. Hexagonal zones. Weak Pl. o>e o= blue, purple, e= blue, blue green, yellowish green, yellow | Hexagonal prismatic. Hexagonal, rectangular sections.Tabular. Inclusions are common. | Basal parting {0001, rhombohedral planes parting {10-11} | Multiple lamellar on {10-11}. Contact twin {10-11} or {0001} | // extinction // to basal parting Symmetrical to rhombohedral parting planes Length fast | Δn='.007-0.010 1st order grey, white, to pale yellow | H(+) no=1.767-1.772 ne=1.759-1.763 | U(-) Also anomalous B(-) Trigonal | Also anomalous B(-) with 2Vx up to 58° | In Al-rich, Si-poor environment. Plutonic igneous, syenite, nepheline syenite, monzonite. In quartz-free pegmatite. Volcanic, in andesite dykes. Metamorphic, mica schist, chlorite schist. In contact zones between igneous rocks and limestone: emery deposits. With spinel, cordierite. sillimanite, garnet, tourmaline, kyanite, rutile, magnetite, ilmenite |
| CRISTOBALITE SiO2 (Oxide, Quartz group) | Colorless | Octahedron, cubic | None | {111} | Δn=0.003 | M(-) no=1.487 ne=1.484 | U(-) Tetragonal (pseudoisometric) | Volcanic. Shallow plutonic. With tridymite, topaz, garnet, fayalite. In serpentinites: lussatite Replaced by quartz | ||
| CROSSITE Na2(Mg,Fe++)3(Al,Fe+++)2Si8O22(OH)2 (Inosilicate, clinoamphibole. Intermediate in the Glaucophane - Riebeckite series: | Colorless to blue Pl. X= colorless, pale blue, yellow, Y= lavender blue, bluish green, Z= blue, greenish blue, violet | Prismatic columnar, bladed, acicular, fibrous | {110} intersects at ~ 55° and 125° | Simple or lamellar on {100} | Inclined ext. less than ~22°. Usually less than 10° Length slow or fast | Δn=0.012-0.016 Middle to upper 1st order | M(+) H(+) nx=1.647-1.690 ny=1.663-1.690 nz=1.663-1.702 | B(+) or B(-) Monoclinic | 2Vx=0°-180° r>v or r<v very strong | Blue schists: metamorphic high -pressure low temperature With lawsonite, garnet, pumpellyite, chlorite, albite, quartz, epidote. Also in eclogites with garnet, hornblende, omphacite. |
| CUMMINGTONITE []Mg7Si8O22(OH)2 (Inosilicate, clinoamphibole: Cummingtonite - Grunerite series) | Colorless, pale green, brown. Color increases with higher Fe content. Weak pleochroism (colored sections) X= colorless, pale yellow, Y=pale yellow, pale brown, Z=pale green, pale brown | Prismatic columnar, bladed, acicular, fibrous. Rhombic basal section | {110} intersects at 56° and 124°. | Cummingtonite: Inclined ext. 15°-21° (010) Length slow. | Δn=0.022-0.035 Up to 2nd order. Δn increases with increasing Fe content. | M(+) H(+) nx=1.632-1.663 ny=1.638-1.677 nz=1.655-1.697 R.I. increases with increasing Fe content. | B (+) Monoclinic B(+): >30-40% Mg, 2Vz=68°-90° B(-): <30-40% Mg, 2V=83°-90° | 2Vz=70°-90° Weak, r<v | Mafic. Metamorphic, amphibolites, gneiss, hornfels, granulite, Diorite. Rare Intermediate volcanics With anthophyllite, gedrite, garnet, cordierite, plagioclase, hornblende, biotite Altered to hornblende, talc, serpentine | |
| CUPRITE Cu2O (Oxide) | Red, orange, yellow. No Pl. | Octahedral, cubic, dodecahedral | {111} fair | VH(+) n=2.849 | Isotropic Cubic | In oxidized zone of hydrothermal Cu deposits With malachite, azurite, copper Altered to malachite, copper | ||||
| DATOLITE CaB(SiO4)OH (Nesosilicate) | Colorless | Massive form | None | None | No consistent elongation shown | Δn=0.044-0.046 Btight 1st order, 2nd order, to middle 3rd order | H(+) nx=1.622-1.626 ny=1.649-1.654 nz=1.666-1.670 | B(-) Monoclinic | 2Vx=72°-75° r>v weak | Cavities in basalt, andesite, diabase, with zeolites, prehnite, calcite, danburite. In contact metamorphic marbles or skarns, with calcite, prehnite, aegirine-augite, fluorite. Rare in granite, serpentinite, basic schists and hydrothermal veins |
| DIOPSIDE CaMgSi2O6 (Inosilicate, calcic clinopyroxene. Diopside - Hedenbergite series) (Di100-Di50) | Colorless, grey, pale green, pale brown, brownish green. Weak Pl pale green, greenish brown, bluish green, yellow green. | Stubby prismatic xls | {110} distinct, intersect at ~87°. Parting {001} and {100} | {100} or {001} lamellar, possible herringbone pattern | Basal (2 cleavages) symmetrical ext. // c: inclined 35°-48° // (100) is length slow | Δn=0.030 2nd order | H(+) nx=1.664-1.672 ny=1.672-1.681 nz=1.694-1.702 R.I. increases with Fe content | B(+) Monoclinic | 2Vz=57°-58° increase with Ca content r>v weak | In calc-silicates marble, skarn, pyroxene granulites.Alkali-olivine basalt and alkali igneous rocks. Cr diopside in ultramafic (kimberlite, peridotite). Metamorphic in Ca-Mg sediments. Altered to uralite, talc, serpentine, chlorite |
| DOLOMITE CaMg(CO3)2 (Carbonate. Dolomite group) | Colorless | Rhombohedrons, curved faces | {10-11} perfect Some deformation twins (if present) bisect obtuse cleavage angle (see calcite) | {02-21} lamellar Simple: {0001}, {10-10}, {11-20}, {10-11} | Symmetrical or inclined | Δn=0.179-0.185 High upper order white or grey | M(-) M(+) H(+) no=1.679-1.703 ne=1.500-1520 | U(-) Hexagonal, Trigonal | In limestone, dolomite. In evaporites. Metamorphic: marble. With calcite, talc, forsterite, tremolite, actinolite, wollastonite. Hydrothermal | |
| DUMORTIERITE Al7(BO3)(SiO4)3O3 (Nesosilicate) | Blue. Pl. X=cobalt blue, violet, red green, brown, Y=colorless, yellow, lilac, green, pale blue or green, Z=colorless, yellow, light blue, light green | Bladed, acicular, prismatic, elongated | {100} good, {110} poor | Cyclic {110}: show ~ hexagonal cross section | Ext.// Length fast | Δn=0.011-0.037 1st order yellow; up to 2nd order Increase with Fe | H(+) nx=1.659-1.686 ny=1.684-1.722 nz=1.686-1.723 | B(-) Orthorhombic, pseudohexagonal | 2Vx=13°-55° | Granitic pegmatite, aplite. Hydrothermal Medium and high grade metamorphic gneiss, quartzite, pelitic schist. With kyanite, sillimanite, cordierite, andalusite Altered to white mica. |
| ECKERMANNITE NaNa2(Mg4Al)Si8O22(OH)2 (Inosilicate, clinoamphibole. Series arfvedsonite - eckermannite) (FERROECKERMANNITE = NaNa2(Fe++Al)Si8O22(OH)2) | Blue green, brown, violet Pl. X= blue green, Y= pale blue green, Z= pale yellowish green | Bladed, prismatic, fibrous. Rhombic basal section. | {110} intersects at 56° and 124°. | Simple or lamellar on {100} | Symmetrical (basal). // (100). Inclined on other longitudinal sections Length fast. | Δn=0.01-0.02. Up to 1st order red | M(+) nx=1.61-1.64 ny=1.62-1.65 nz=1.63-1.66 | B(-) Monoclinic | 2Vx=15°-80° | In alkaline igneous rocks: granite, syenite, trachyte, phonolite, pegmatite. With aegirine, aegirine-augite, biotite, feldspar, nepheline. Altered to uralite, iron oxides, carbonates. |
| ENSTATITE (En100-En88) Mg2Si2O6 (Inosilicate, orthopyroxene. Enstatite - Ferrosilite series) | Colorless. Pale colored. No or weak Pl. | Stubby prismatic. Basal sections 6 or 8 sides, showing cleavages. Exsolution lamellae (augite) | Good // {210}, intersect at ~ 88°. Parting on {100}, {010} and {001} with exsolution lamellae (augite) | Fine lamellar // {100} is often exsolution lamellae | Ext. //. Basal: symmetrical Cleavage trace length slow. | Δn=0.008-0.011 Up to 1st order yellow | M(+) H(+) En100: nx=1.654 ny=1.655 nz=1.665 | B(+) Orthorhombic | 2Vz=35°-90° r>v weak | In gabbro, pyroxenites, peridotites, dunites, serpentinites. With olivine, Mg-rich clinopyroxenes phlogopite, plagioclase. Altered to serpentine, amphibole, magnesite, talc |
| EPIDOTE Ca2Al2Fe+++[Si2O7][SiO4]O(OH) (Sorosilicate. Clinozoisite - Epidote series) (There is also Epidote-Pb and Epidote-Sr) | Light yellow green. Pleochroism colorless to yellow. Bright interference colors unevenly distributed. Piemontite: pink Pl. X= colorless, pale yellow, pale green, Y= greenish yellow, Z= pale yellowish green | Prismatic, columnar, bladed, acicular. Radiated, sheaf aggregates. Sections rectangular or 6 sided. | {001} perfect, {100} poor | Lamellar {100} | Inclined ext. 20°-40° Z/\x Length slow | Δn=0.015-0.051 1st order, 2nd order, Also 3rd order bluish or yellowish. Concentrically zoned | H(+) nx=1.715-1.751 ny=1.725-1.784 nz=1.794-1.797 | B(-); also B(+) Monoclinic | 2Vx=64°-95° r>v strong | Metamorphic green schists. Blue schists. In quartzite, slate, phyllite, chlorite schist, mica schist, gneiss, skarn, hornfels. In igneous rocks. Hydrothermal. Plagioclase, biotite, hornblende, clinopyroxene may be altered to epidote. |
| EULITE (En30-En12) (Fe++,Mg)2Si2O6 (Inosilicate, orthopyroxene. Enstatite - Ferrosilite series) (A variety of Ferrosilite) | Colorless, pale colored. Pl. X= brown, Y= yellow, yellow, Z= blue green | Stubby prismatic. Basal sections 6 or 8 sides, showing cleavages | Good // {210}, intersect at ~ 88°. Parting on {100}, {010} and {001} | {101} | Ext. //. Basal: symmetrical Cleavage trace length slow | Δn=0.018-0.020 Up to lower 2nd order | H(+) nx=1.734-1.755 ny=1.747-1.765 nz=1.752-1.775 | B(+) Orthorhombic | 2Vz=62°-90° v>r moderate | In metamorphosed Fe sediments with Fe-olivine, diorites, monzonites. Altered to bastite, uralite. |
| FAYALITE Fe++2SiO4 (Nesosilicate. Fo0-Fo50 olivine forsterite - fayalite series) | Colorless to pale yellow, red brown. PL. X=Z= pale yellow, Y= orange brown, yellowish brown, reddish brown | Bipyramidal, stubby prismatic | {010} distinct {110} poor, usually not seen | {100}, {011}, {012}: simple {031} cyclic | Ext. // (elongated xls) Length fast or length slow | Δn=0.052 3rd order | H(+) nx=1.734-1.827 ny=1.760-1.869 nz=1.778-1.879 R.I. increases from Fo100 to Fo0 | B(-) Orthorhombic | 2Vx=46°-72° r>v weak 2Vx decreases from Fo100 to Fo0 | Fe rich: plutonic, volcanic. In syenite, nepheline syenite, phonolite, trachyte, andesite, dacite. Mg Fe: plutonic, volcanic, mafic, ultramafic. In gabbro, pyroxenite, peridotite, dunite Mn rich: In Fe Mn deposits, skarns Altered to serpentines, iddingsites. |
| FERRO-ACTINOLITE []Ca2Fe++5Si8O22(OH)2 (Inosilicate. Clinoamphibole, Tremolite - Actinolite - Ferro-actinolite series.). | Dark green to black. Color increases with Fe content. Pl. X=colorless, pale yellow green, Y=pale yellow green, pale blue green, green Z= pale green, green, blue-green, dark green | Prismatic columnar, bladed, acicular, fibrous. Rhombic basal section. | {110} intersects at 56° and 124°. Visible on basal sections | Simple or {100} lamellar, // to the long diagonal of basal section. | Inclined 12°-18°. Sections // to (100) show // extinction Length slow. | Δn=0.018-0.019 Upper 1st order to mid 2nd order | H(+) nx=1.669-1.686 ny=1.680-1.696 nz=1.688-1.704 R.I. increases with increasing Fe content. | B(-) Monoclinic | 2Vx=63°-75° r<v weak | Metamorphic rocks and regional contact metamorphic. Altered to chlorite, talc, amphibole. |
| FERROHYPERSTHENE (En50-En30) (Fe++,Mg)2Si2O6 (Inosilicate, orthopyroxene. Enstatite - Ferrosilite series) (A variety of Ferrosilite) | Pale colored, pinkish to greenish. Pl. X= salmon pink, Y= yellow, Z= blue green | Stubby prismatic. Basal sections 6 or 8 sides, | {110} distinct intersect at ~87°. Parting on {010} and {001}. | {101} | Ext. //. Basal: symmetrical Cleavage trace length slow | Δn=0.015-0.018 1st order | H(+) nx=1.710-1.734 ny=1.722-1.747 nz=1.725-1.752 | B(+) Orthorhombic | 2Vz=53°-62° v>r weak | In gabbro, diorite, monzonite. In metamorphosed Fe-sediments Altered to bastite, uralite (fibrous actinolite-tremolite) |
| FERROSILITE (En12-En0) (Fe++,Mg)2Si2O6 (Inosilicate, orthopyroxene. Enstatite - Ferrosilite series) | Deep green to brown. Pl. | Stubby prismatic. Basal sections 6 or 8 sides, showing cleavages | Good // {210}, intersect at ~ 88°. Parting on {100}, {010} and {001} with exsolution lamellae (augite) | {101} | Ext. //. Basal: symmetrical Cleavage trace length slow | Δn=0.015-0.022 Up to lower 2nd order | H(+) nx=1.755-1.768 ny=1.765-1.771 nz=1.775-1.188 | B(+) Orthorhombic | 2Vz=90°35° r>v strong | Thermal metamorphism of Fe-rich rocks |
| FLUORITE CaF2 (Halide) | Colorless, bluish, purplish, pinkish, greenish. No Pl. | Cubic, octahedral, dodecahedral. | {111} perfect octahedral | Penetration twins {111} | M(-) n=1.433-1.435 | Isotropic Cubic | Hydrothermal deposits, with sulfides. Granite, syenite, granitic pegmatite. In carbonate sediments. Cementing clastic sediments. | |||
| FORSTERITE Mg2SiO4 (Nesosilicate. Fo100-Fo50, olivine forsterite - fayalite series) | Colorless to pale green No Pl. | Bipyramidal, stubby prismatic | {010}, {110}: poor | {100}, {011}, {012}: simple {031} cyclic | Ext. // (elongated xls) Length fast or length slow | Δn=0.035 - 0043 2nd order | M(+) H(+) nx=1.635-1.73 ny=1.651-1.76 nz=1.670-1.77 R.I. increases from Fo100 to Fo0 | B(+) Orthorhombic Also B(-) | 2Vx=72°-98° v>r or r>v, weak 2V decreases from Fo100 to Fo0 | Mg rich: with calcite, dolomite, diopside, epidote, grossular, tremolite Mg Fe: plutonic, volcanic, mafic, ultramafic. In gabbro, pyroxenite, peridotite, dunite Altered to serpentines, iddingsites. |
| GARNET group (Nesosilicates. Garnet group) Pyralspites: Pyrope Mg3Al2(SiO4)3 Almandine Fe3Al2(SiO4)3 Spessartine Mn3Al2(SiO4)3 Ugrandites: Grossular Ca3Al2(SiO4)3 Andradite Ca3Fe2(SiO4)3 Uvarovite Ca3Cr2(SiO4)3 Hydrogrossular Ca3Al2(SiO4)3-x(OH)4x | Colorless, pale colored, reddish, pinkish, greenish, yellowish. No Pl. | Dodecahedral {110}, trapezohedral {112}. 6 or 6 sided cross section. Quartz inclusions | Parting // to dodecahedral {110} faces | No twinning | H(+) n=1.72-1.77 Pyrope n=1.77-1.82 Almandine n=1.79-1.81 Spessartine n=1.735-1.77 Grossular n=1.85-1.89 Andradite n=1.838-1.87 Uvarovite n=1.675-1.734 Hydrogrossular | Isotropic Cubic | Metamorphic. Mica schists, gneiss, pegmatite, granite, felsic igneous: Almandine Ultramafic igneous rocks, peridotites, serpentinites: Pyrope Granite, pegmatite, felsic igneous: Spessartine Skarn: Grossular. With calcite, dolomite, wollastonite, tremolite, epidote Skarn, hydrothermal veins: Andradite Cr igneous rocks, peridotite: Uvarovite Altered to chlorite, actinolite,hornblende, epidote, iron oxides, biotite | |||
| GEDRITE [](Mg,Fe++)5Al2Si6Al2O22(OH)2 (Inosilicate, orthoamphibole) (There is also Ferrogedrite, Sodiumgedrite) | Pale brown, yellow-brown, greenish brown. Darker when Fe increases. No or weak Pl. X=Y= pale yellowish, pale greenish, greyish brown, Z= yellowish brown, greenish grey, greyish brown, purplish brown. | Prismatic columnar, bladed, acicular, fibrous. Rhombic basal section. | {210} intersects at 55° and 125°. | Symmetrical (basal). // (longitudinal) Length slow. | Δn=0.016-0.028 1st order red, 2nd order blue, green. Birefringence increasing with Fe content. | M(+) H(+) nx=1.615-1.694 ny=1.625-1.710 nz=1.634-1.722 | B(+) or B(-) Orthorhombic | 2Vz=57°-108° Weak, r<v (+), r>v (-) | Medium and high grade metamorphic: amphibolite, gneiss, granulite, hornfels, talc schist. With garnet, cordierite, anthophyllite, hornblende, sillimanite, plagioclase. Altered to serpentine, talc. | |
| GLAUCONITE (K,Na)(Mg,Fe++,Fe+++)(Fe+++,Al)(Si,Al)4O10(OH)2 (Phyllosilicate, mica group) | Green. Al-rich glauconite: pale green, colorless Distinct Pl. X= yellowish green, green, Y=Z= green, bluish green, darker yellowish green | Granules, micaceous, flakes | {001} perfect often not visible since too fine grained | // extinction to cleavage Trace of cleavage: length slow | Δn=0.02-0.03 Upper 1st order, 2nd order | M(+) nx=1.59-1.61 ny=1.61-1.64 nz=1.61-1.64 | B(-) Monoclinic Basal sections almost isotropic | 2Vx=0°-20° | Granules in detritical sediments of marine origin "greensands". Altered to limonite and goethite. | |
| GLAUCOPHANE []Na2(Mg3Al2)Si8O22(OH)2 (Inosilicate, clinoamphibole. Glaucophane - Riebeckite series) (There is also Ferroglaucophane) | Colorless to blue, lavender blue, pale bluish green Pl. X= colorless, pale blue, yellow, Y= lavender blue, bluish green, Z= blue, greenish blue, violet | Bladed, prismatic, fibrous (crocidolite). Rhombic basal section. | 2 cleavages {110} intersect at ~ 58° and ~122° | Simple or lamellar on {100}, not common. | Inclined ext. less than ~22° According to Tröger: 5°-10° Length slow. | Δn=0.008-0.029 Middle to upper 1st order and beginning 2nd order. | M(+) nx=1.594-1.647 ny=1.612-1.663 nz=1.618-1.663 | B (-) Monoclinic | 2Vx=10°-50° r<v weak | Blue schists: metamorphic high pressure low temperature With lawsonite, garnet, pumpellyite, chlorite, albite, quartz, epidote. Also in eclogites with garnet, hornblende, omphacite, clinozoisite. |
| GRUNERITE []Fe++7Si8O22(OH)2 (Inosilicate, clinoamphibole. Cummingtonite - Grunerite series) (There is also Manganogrunerite) | Colorless, pale green, brown. Color increases with higher Fe content. Weak pleochroism (colored sections) X= colorless, pale yellow, Y=pale yellow, pale brown, Z=pale green, pale brown | Prismatic columnar, bladed, acicular, fibrous. Rhombic basal section. | {110} intersects at 56° and 124°. | Simple and lamellar {100} | Inclined 10°-20° Length slow. | Δn=0.036-0.044 Up to mid 3rd order. Δn increases with increasing Fe content. | H(+) nx=1.664-1.688 ny=1.682-1.712 nz=1.700-1.732 R.I. increases with increasing Fe content. | B (-) Monoclinic | 2Vz=80°-90° Weak, r>v | Metamorphic. With magnetite, quartz. Altered to hornblende, talc, serpentine |
| GYPSUM CaSO4.2H2O (Sulfate) | Colorless Zoning | Tabular, prismatic, acicular | {010} perfect, {100} good, {111} good Intersect at 42° and 138° | Simple contact twins {100} (butterfly twins) | Maximum inclined ext. angle seen on {010}: ~38° to {100} cleavage | Δn=0.010 weak 1st order grey, white, pale yellow | L(-) nx=1.519-1.521 ny=1.522-1.526 nz=1.529-1.531 | B(+) Monoclinic | 2Vz=58° | In evaporites, with halite, sylvite, anhydrite, calcite, dolomite, clay. Anhydrite hydrates to become gypsum Pseudomorphs after anhydrite, calcite, halite. Replaced by chalcedony, opal, calcite, aragonite, anhydrite, celestite. |
| HAUYNE (Na,Ca,K)8-4(SO4)2-1(AlSiO4)6 (Hauÿne. Tectosilicate, feldspathoid, sodalite group) | Blue, colorless. Irregularly colored. Dark rim: "Trauerrand". No Pl. | Dodecahedral, six sided cross section | {110} poor dodecahedral | {111} seldom | M(-) n=1.494-1.509 | Isotropic Cubic | In Si-deficient volcanic: phonolite, alkaline basalt, feldspathoid basalt, trachyte. Plutonic. With nepheline, leucite, sanidine. Altered to zeolite (fibrous), clay, calcite, cancrinite. | |||
| HEDENBERGITE CaFe++Si2O6 (Inosilicate, calcic clinopyroxene. Diopside - Hedenbergite series) (Di50- Di0) | Colorless, grey, pale green, pale brown, brownish green. No or Weak Pl pale green, greenish brown, bluish green, yellow green. | Prismatic, radiated columnar, acicular xls | {110} distinct, intersect at ~87°. Parting {001} and {100} | {100} or {001} lamellar, possible herringbone pattern (rare) | Basal (2 cleavages) symmetrical ext. // c: inclined 35°-48° // (100) is length slow | Δn=0.028-0.029 Up to second order. | H(+) nx=1.722-1.728 ny=1.730-1.736 nz=1.750-1.757 R.I. increases with Fe content | B(+) Monoclinic | 2Vz=62°-63° increase with Ca content r>v strong | Skarns and siliceous hornfels with grunerite. Alkali granites. |
| HEMATITE Fe2O3 (Oxide) | Opaque mineral. Deep brown red on very thin xls or edges. Pl. o=brownish red, e=yellowish red or brown, o>e | Tabular, hexagonal, fibrous, botryoidal, scaly, etc. | Basal parting {001}, rhombohedral parting {101} | None | Ext // to basal parting | Δn=0.28 High upper order | VH(+) no=3.15-3.22 ne=2.87-2.94 | U(-) Hexagonal, Trigonal | Common Fe-oxide in all rock types. | |
| HEULANDITE (Ca0,5,Na,K)9[Al9Si27O72].24H2O (Tectosilicate, zeolite, heulandite - stilbite - brewsterite group) )There is Heulandite-Ba, -Ca, -K, -Na, -Sr) | Colorless | Tabular // (010), trapezohedral outline | {010} perfect | ~// extinction to the trace of cleavage Sections cut // {010} show inclined ext. to xl outlines (no cleavage) Length fast on cleavage trace | Δn=0.006-0.009 | M(-) L(-) nx=1.492-1.505 ny=1.494-1.506 nz=1.501-1.512 | B(+) Monoclinic | 2Vz= ~ 30° (=°-50°) r>v | In lacustrine sediments. In basalt, gabbro, serpentinite. Volcanic altered rocks. | |
| HORNBLENDE []Ca2[Fe++4(Al,Fe+++)]Si7AlO22(OH)2 (Inosilicate, clinoamphibole, a series name) (There is Ferrohornblende, Magnesiohornblende) | Green, yellow-green, blue-green, brown Pl. green hornblende: X= light yellow, light yellow green, light blue green, Y= green, yellow green, grey green, Z= dark green, dark blue green, dark grey green Pl. brownish hornblende: X= yellow, greenish yellow, light greenish brown, Y= yellow brown, brown, reddish brown, Z= grey brown, dark brown, reddish brown | Prismatic, bladed. Rhombic basal section. | 2 cleavages {110} intersect at 56° and 124°. | Simple and lamellar on {100} | Symmetrical (basal). Sections // (010): inclined 12°-34° (often 14°-25°) Length slow | Δn=0.014-0.034 (often 0.018-0.028) Upper 1st order to lower 2nd order | M(+) H(+) nx=1.60-1.70 ny=1.61-1.71 nz=1.62-1.73 | B(+) or B(-) Monoclinic | 2Vx=35°-130° (often about 75°) | Ubiquitous. Igneous plutonic, volcanic, mafic, metamorphic: diorite, andesite, rhyolite, gabbro. Metamorphic: amphibolite, marble, skarn Altered to uralite, chlorite, biotite |
| HUMITE (Mg,Fe++)7(SiO4)3(F,OH)2 (Nesosilicate, humite group) | Colorless, pale yellow, yellow, orangish yellow. Darker color when Fe, Ti increase Weak Pl. X= very pale yellow, dark yellow, Y= colorless, pale yellow, Z= colorless, pale yellow | Grains. Platy xls | {100} | Simple or multiple twins | Either length fast or length slow | Δn=0.029-0.036 Bright upper 2nd order | M(+) H(+) nx=1.607-1.643 ny=1.619-1.655 nz=1.639-1.675 | B(+) Orthorhombic | 2Vz=65°-84° r>v | In contact metamorphic limestone and dolomite. In skarns. With tremolite, wollastonite, grossular, monticellite, forsterite, calcite, dolomite In mafic igneous rocks Altered to serpentine, chlorite |
| HYALOPHANE (K,Ba)Al(Si,Al)3O8 (Tectosilicate. Ba feldspar) | Colorless | Tabular, prismatic, elongated xls | {001} perfect, {010} distinct, intersecting at 90°. {110} poor | Simple, Carlsbad, Manebach, Baveno. No multiple twinning. | Max.0°-19°° on {001} cleavage | Δn=0.005-0.010 1st order grey, white or pale yellow | L(-) to L(+) nx=1.520-1.542 ny=1.524-1.545 nz=1.526-1.547 | B(-) Monoclinic | 2Vz=48°-79° r>v | Hydrothermal veins in rich Mn rocks. Granite gneiss. With Mn minerals, rhodonite, rhodochrosite, spessartine |
| HYPERSTHENE (En70-En50) (Mg,Fe++)2Si2O6 (Inosilicate, orthopyroxene. Enstatite - Ferrosilite series) | Pale colored, pinkish to greenish. Pl. X= pink, brownish pink, pale yellow, Y= light brown, yellow, pinkish yellow, greenish yellow, Z= light green, grey green, bluish green | Stubby prismatic. Basal sections 6 or 8 sides, showing cleavages Exsolution lamellae (augite). | Good // {210}, intersect at ~ 88°. Exsolution lamellae (augite) Parting on {010} and {001}. | Fine exsolution exsolution lamellae // (100) | Ext. //. Basal: symmetrical Cleavage trace length slow | Δn=0.008-0.020 1st order | H(+) nx=1.699 ny=1.711 nz=1.714 | B(+) Orthorhombic | 2Vz=50°-57° | Plutonic and volcanic. In norite, gabbro. Ferrohypersthene in diorite, monzonite, granite. xls of orthopyroxene surrounded by a rim of clinopyroxene. |
| ILLITE K0,65Al2[]Al0,65Si3,35O10(OH)2 (Phyllosilicate, hydromica group; a clay mineral) | Colorless | Fine crystalline. | {001} perfect, normally not visible | Extinction ~ // Length slow | Δn=0.020 | L(+) M(+) nx=1.53-1.57 ny=1.56-1.61 nz=1.56-1.61 | B(-) Monoclinic | 2Vx<10°, often not possible to determine. | Common in diagenetic to low-grade sedimentary rocks. In alkali granites. In ore veins. It alters K-feldspar, muscovite, kaolinite. | |
| JADEITE Na(Al,Fe+++)Si2O6 (Inosilicate, sodic clinopyroxene) | Colorless Pl. pale green, yellow | Stubby prismatic. Acicular. Basal sections 4 or 8 sides | {110} intersect at ~87° | Simple or lamellar {100} or {001} | Basal (2 cleavages) symmetrical ext. Longitudinal // (100) Inclined 32°-55° in (010) sections Length slow | Δn=0.006-0.021, often 0.012-0.018 1st order yellow or red, also 2nd order | M(+) H(+) nx=1.640-1.681 ny=1.645-1.684 nz=1.652-1.692 | B(+) or B(-) Monoclinic | 2Vz=60°-96°, often ~70° r>v weak to very strong | In high pressure metamorphic rocks: glaucophane schist, serpentinite. With albite, glaucophane, actinolite,lawsonite, quartz, chlorite, garnet, zoisite, mica, calcite, aragonite, Altered to amphibole |
| JOHANNSENITE CaMn++Si2O6 (Inosilicate, clinopyroxene) | Colorless | Stubby prismatic, radiated acicular. | {110} distinc tParting on {100} or {001}. | Simple or lamellar {100} | Δn=0.029 | nx=1.703-1716 ny=1.711-1.716 nz=1.732-1.745 | B(+) | 2V=68°-73° r>v moderate | Limestone contact zones with rhodonite. In rhyolite. Alterates to rhodonite, xonotlite | |
| KAERSUTITE NaCa2(Mg4Ti)Si6Al2O23(OH) (Inosilicate, clinoamphibole) (There is also Ferrokaersutite) | Yellowish, reddish, greenish brown, fox brown. Strong Pl. X= yellow, brownish yellow, Y= reddish brown, Z= dark reddish brown, greenish brown | Prismatic, bladed. Rhombic basal section. Often Color zoned | {110} intersects at 56° and 124°. | Simple or lamellar on {100} | Symmetrical (basal). Inclined 0°-19° Length slow | Δn=0.02-0.08. 2nd order to 4th order, 5th order. Birefringence increasing with Fe content. | H(+) nx=1.67-1.71 ny=1.69-1.74 nz=1.70-1.77 | B(-) Monoclinic | 2Vx=66°-82° r>v strong | Alkaline rocks. Volcanic: trachyte. Intrusive: monzonite, syenite With titanite, Ti augite, Ti biotite, Fe Ti oxides Alteration: amphiboles, Ti augite, chlorite, Fe Ti oxides |
| KAOLINITE Al2Si2O5(OH)4 (Phyllosilicate clay mineral group) | Colorless, greyish, brownish, ~ opaque Pl. weak. | Often cloudy aggregate mass | {001} perfect, normally not visible. | Ext. // Occasional slight inclined on (010) | Δn=0.005-0.008 1st order low grey Montmorillonite clays show higher Δn than kaolinite clays. | L(+) nx=1.553-1.565 ny=1.559-1.569 nz=1.560-1.570 | B(-) Difficult to obtain figures Triclinic (Kaolinite-1A) Monoclinic (Kaolinite-1M) Often almost isotropic | 2Vx=23°-60° r>v weak Often not possible to determine | Altered to feldspars and Al-minerals, diaspore, gibbsite. | |
| KYANITE Al2SiO5 (Disthen. Nesosilicate sillimanite - andalusite - kyanite group) | Colorless, light blue, pale greyish pinkish brown Pl. weak X= colorless, Y=light violet blue, Z=light cobalt blue | Prismatic, elongated on c, Bladed xls, bent xls | {100} perfect. {010} good, intersect at 74° Basal parting {001} ~ right angle to xl length. | Simple or multiple on {100}. Multiple on {001} | Inclined ext. max. 30° 7° on section // (010) 3° on basal section Length slow | Δn=0.012-0.016 1st order yellow. | H(+) nx=1.710-1.718 ny=1.719-1.725 nz=1.724-1.734 | B(-) Triclinic | 2Vx=78°-84° r>v weak | Metamorphic, mica schist, gneiss. Rarely in granitic pegmatite, eclogite, kimberlite. With staurolite, sillimanite, andalusite, chloritoid, garnet Altered to chlorite, margarite, pyrophyllite |
| LABRADORITE (Ca,Na)[Al(Al,Si)Si2O8] (Tectosilicate. plagioclase, An50-An70) | Colorless, clouded (alteration) | Tabular, // to (010), prismatic, elongated. Common chemical zoning | {001} perfect, {010} good, {110} poor | Albite polysynthetic. Pericline polysynthetic. Carlsbad penetration | Inclined. Michel-Lévy method or Carlsbad-Albite method Calculate with Ch. de Capitani | Δn=0.008. Low: 1st order up to white Optic related to anorthite content | L(+) nx=1.560 ny=1.564 nz=1.568 | B(+) Triclinic | 2Vx=80° r>v weak | In gabbro, anorthosite, mafic rocks. Volcanic: basalt Altered to calcite, sericite, zeolites, muscovite, paragonite, kaolinite, scapolite, prehnite, pyrophyllite |
| LAUMONTITE Ca4[Al8Si16O48].18H2O (Tectosilicate, zeolite, laumontite - yugarawalite group) | Colorless | Prismatic, fibrous | {010} and {110} intersect | // {100} | Ext. 8°-33° in sections cut // (010) Length slow Basal sections: ext. // to {010} cleavage and symmetrical to {110} cleavage | Δn=0.010-0.012 1st order white | L(-) nx=1.502-1.514 ny=1.512-1.522 nz=1.514-1.525 | B(-) Monoclinic | 2Vx=26°-47° r<v | In lacustrine sediments. In basalt, gabbro, serpentinite. Volcanic altered rocks. Low grade metamorphic rocks. Altered to zeolites. |
| LAWSONITE CaAl2Si2O7(OH)2.H2O (Sorosilicate, lawsonite group) | Usually colorless. Pl. X=light blue, brownish yellow, Y=yellow, yellow green, blue green, Z=colorless, light yellow | Tabular, rhombic, rectangular, prismatic, acicular | 2 perfect cleav. {010} and {100} intersect at right angles. 2 imperfect // {101} intersect ~ 67° | Lamellar // {101} | // extinction | Δn=0.019-0.021 1st order, beginning 2nd order | M(+) H(+) nx=1.663-1.665 ny=1.672-1.675 nz=1.682-1.686 | B(+) Orthorhombic | 2Vz=76°-87° | In glaucophane schists with pumpellyite, chlorite and albite. |
| LEPIDOLITE K(Li,Al)3(Si,Al)4O10(F,OH)2 (Phyllosilicate, Li-mica, mica group) | Colorless, pale pink, pale green Pl. pink, violet, green shades | Tabular // (001), hexagonal outline, flakes | {001} perfect | ~ // to cleavage, inclined 0°-7° Length slow | Δn=0.018-0.038 2nd order (muscovite: ~ higher birefringence) | L(+) M(+) (Muscovite: greater relief) nx=1.525-1.548 ny=1.548-1.585 nz=1.554-1.587 | B(-) Monoclinic | 2Vx=0°-58° (often 30°-50°) r>v | In granitic pegmatites with quartz, K-feldspar, albite, beryl, tourmaline, spodumene May be replaced by muscovite | |
| LEUCITE K[AlSi2O6] (Tectosilicate. Feldspathoid) | Colorless. Clouded. | Trapezohedral xls, 8 sided section. Oriented inclusions "Schlackenkränzchen" | {110} very poor, pseudododecahedral | Thin lamellar twins // {110}, arranged ~ concentrically | No elongation. | Δn=0.000-0.001 Lower 1st order grey. | L(-) no=1.508-1.511 ne=1.509-1.511 | U(+) Tetragonal (pseudocubic, almost isotropic) | Si-deficient volcanic: leucophonolite, leucotephrite, leucitite. With olivine, nepheline, sanidine, clinopyroxene, phlogopite, apatite, Na Ca amphiboles. Altered to pseudoleucite, a mixture. | |
| MALACHITE Cu2(CO3)(OH)2 (Carbonate) | Green Pl. X=almost colorless, pale green, Y=yellowish green, Z=dark green | Concentric color banding, fibrous, botryoidal | Difficult to see. {-201} perfect, {010} fair | {100} common (difficult to see) | Inclined ext. Length fast. | Δn=0.254 High order(masked by mineral color) | M(+) H(+) nx=1.655 ny=1.875 nz=1.909 | B(-) Monoclinic | 2Vx=43° r<v | In oxidized zone of hydrothermal Cu deposits Altered to azurite, cuprite. |
| MAGNESITE MgCO3 (Carbonate, calcite group) | Colorless. Cloudy. | Rhombic, prismatic, lamellar, fibrous | Rhombohedral {10-11} perfect | Rare translation gliding on {0001} No twin lamellae | Extinction symmetrical to basal cleavage traces or inclined | Δn=0.191 High order | L(-) L(+) M(+) H(+) no=1.700 ne=1.509 | U(-) Hexagonal, Trigonal | Alteration of Mg-rich rocks: serpentinite, peridotite, pyroxenite, dunite. Metamorphic. Sedimentary. | |
| MELILITE group (Ca,Na)2(Al,Mg)(Si,Al)2O7 (Sorosilicate. Includes Akermanite, Gehlenite, etc.) | Colorless, pale yellow Weak pleochroism o>e o= golden brown e=pale yellow | Tabular // (001). Square, octagonal cross section. Rod inclusions // c | {001} | Ext. // in rectangular sections. Length slow | Δn=0.001-0.013 Lower 1st order to mid 1st order; anomalous Berlin blue colors. | M(+) H(+) no=1.624-1.666 ne=1.616-1.661 | U(-) or U(+) Tetragonal Gehlenite U(-) Akermanite U(+) | In Si deficient mafic rocks. With Ca plagioclase, olivine, clinopyroxene, nepheline, leucite (in volcanic). Akermanite found in high-grade metamorphic carbonate rocks With melanite (in plutonic). Not with quartz. Altered to fibrous cebollite, zeolites, calcite. | ||
| MICROCLINE KAlSi3O8 (Tectosilicate. K feldspar) | Colorless. Brownish alteration. Perthitic | Tabular and prismatic elongated xls. | {001} perfect, {010} good, intersect at 91° | Albite + pericline: cross-hatched twin pattern: "tartan plaid" (anorthoclase is similar to microcline, but has ultra-fine twinning) | Inclined 15° on {001} cleavage. Inclined 5° on {010} cleavage. Inclined 12° in cryptoperthites | Δn=0.005-0.008 Low: up to 1st order grey | L(-) nx=1.514-1.516 ny=1.518-1.519 nz=1.521-1.522 | B(-) Triclinic | 2Vx=~65°-88° | Plutonic felsic igneous: granite, granodiorite, pegmatite, syenite. Metamorphic: gneiss. Authigenic in sedimentary rocks and hydrothermal veins: triclinic adularia with rhombic cross section. Altered to sericite and clay. |
| MONTICELLITE CaMgSiO4 (Nesosilicate, monticellite series) | Colorless | Grains, polygonal sections | {010} poor | {031} cyclic twins | Elongate xls: length slow or long fast | Δn=0.012-0.020 up to 1st order red | M(+) H(+) nx=1.638-1.654 ny=1.646-1.664 nz=1.650-1.674 | B(-) Orthorhombic | 2Vx=69°-88° r>v | In contact metamorphic limestone and dolomite. In skarns. With calcite, dolomite, diopside, tremolite, forsterite, wollastonite. In mafic igneous rocks |
| MONTMORILLONITE (Na,Ca)0,3(Al,Mg)2Si4O10(OH)2.nH2O (Phyllosilicate. Clay mineral formerly smectite. Montmorillonite - vermiculite group) | Colorless, pale yellow, pinkish, brownish, ~ opaque (Nontronite is bright green) | Flakes | {001} perfect | Not visible | Extinction ~ // Length slow | Δn=0.01-0.04 Bright colors 2nd order. Montmorillonite clays show higher Δn than kaolinite clays | M(-) L(-) L(+) M(+) nx=1.48-1.57 ny=1.50-159 nz=1.50-1.60 | B(-) Monoclinic | 2V=0° to 30° | Alteration of igneous rocks in semiarid climates. Siliceous rocks tend to yield illite; mafic tend to yield montmorillonite. Altered to kaolinite |
| MORDENITE (Na2,Ca,K2)4(Al8Si40)O96.28H2O (Tectosilicate, zeolite group) | Colorless | Radiate, acicular fibrous | {010} and {100} perfect | None | Δn=0.002-0.005 | nx=1.472-1.483 ny=1.475-1.485 nz=1.477-1.487 | B(-) Orthorhombic | 2V=76° to 90° | Amygdules in volcanic rocks | |
MUSCOVITE | Colorless. Rarely pale pink or green. | Tabular {001}, bladed, hexagonal outline not often seen. Flakes striated with 1 perfect cleavage | {001} perfect, seldom visible | Rare on {001} | Ext. // cleavage. Inclined ext. <3°. Undulatory ext., Pebbly, birds-eye texture seen near extinction Length slow // to cleavage. | Δn=0.035-0.049 high: up to upper 2nd order vivid colors, also 3rd order | L(+) M(+) nx=1.552-1.576 ny=1.582-1.615 nz=1.587-1.618 | B(-) Monoclinic | 2Vx=28°-47° Phengite 2V=0°-20° Paragonite 2V=0°-40° (Colorless lepidolite and talc: smaller 2V. Colorless pyrophyllite: greater 2V) r>v | Felsic plutonic. Granite, granodiorite, aplite, pegmatite. Metamorphic, slate, schist, gneiss, hornfels, phyllite, quartzite Phengite and paragonite in low grade metamorphic rocks. Sericite: hydrothermal alteration of feldspars. |
MYRMEKITE | In metamorphic and granitic rocks | |||||||||
| NATROLITE Na2[Al2Si3O10].2H2O (Tectosilicate, zeolite, natrolite group) | Colorless | Prismatic, acicular. Square cross section | {110} perfect | {110}, {001}, {031} Rare | Ext. //. Basal section: symmetrical ext. Length slow | Δn=0.012-0.013 White, grey, to 1st order yellow | M(-) nx=1.473-1.483 ny=1.477-1.486 nz=1.485-1.496 | B(+) Orthorhombic (pseudotetragonal) | 2Vz=58°-64° r<v weak | In mafic low grade metamorphic and hydrothermal. In altered volcanic rocks with other zeolites, analcime, stilbite, chabazite, heulandite, laumontite |
| NEPHELINE (Na,K)AlSiO4 (Tectosilicate, feldspathoid) | Colorless, cloudy | Stubby prismatic, rectangular. Square or hexagonal cross section. | // {100} // {001} Usually not seen. | {100}, {112}, {335}, usually not seen | Ext. // | Δn=0.003-0.006 1st order, low: up to dark grey | L(-) nx=1.529-1.551 ny=1.526-1.547 | U(-) Hexagonal | In silica undersaturated alkali magmatic rocks. In volcanic rocks. With leucite, aegirine-augite, melanite, melilite, olivine, Ti-augite, Ti-biotite, apatite, cancrinite, feldspars. Altered to sodalite, analcite, cancrinite, fibrous zeolite, sericite | |
| NOSEAN Na8Al6Si6O24(SO4).H2O (Tectosilicate, feldspathoid, sodalite group) | Colorless, grey, grey brown, very pale blue. Dark rim. No Pl. | Six sided hexagonal cross section | Poor {110} | {111} seldom | M(-) n=1.460-1.495 | Isotropic Cubic | In silica deficient alcalic igneous rocks. Altered to zeolite (fibrous), clay, calcite, cancrinite. In volcanic rocks. | |||
| OLIGOCLASE (Na,Ca)(Si,Al)4O8 (Tectosilicate, plagioclase, An10-An30) | Colorless, clouded (alteration). | Tabular, // to (010), prismatic elongated. Common chemical zoning. | {001} perfect, {010} good, {110} poor | Albite polysynthetic. Pericline polysynthetic. Carlsbad penetration | Inclined. Michel-Lévy method or Carlsbad-Albite method Calculate with Ch. de Capitani | Δn=0.008 1st order grey or white; Optic related to anorthite content | L(-) to L(+) nx=1.538 ny=1.542 nz=1.546 (Data for An20) | B(+) or B(-) Triclinic | 2Vx=87° r>v weak (Data for An20 oligoclase low temp.) | In plutonic rocks, granite, granodiorite, pegmatites, syenite. Metamorphic medium and high grade. Volcanic: rhyolite. Altered to calcite, sericite, zeolites, muscovite, paragonite, kaolinite, scapolite, prehnite, pyrophyllite |
| OBSIDIAN A volcanic glass containing crystallites of feldspar, tridymite, cristobalite | Colorless, pale grey, pale yellow brown | n=1.482 (0 weight % H2O), 1.486 (0.35 weight % H2O) | Isotropic | Volcanic. Rhyolitic lava | ||||||
| OLIVINE (Nesosilicates series name. See Fayalite, Forsterite) | Colorless, pale yellow; darker with higher Fe, reddish or black due to impurities | Bipyramidal, stubby prismatic. Grains. 6 or 8 sided | Poor cleavage {010}, {110 usually not seen}. Irregular fractures with alteration. | Rare simple twinning {100}, {011}, {012} | // ext. Length fast or length slow | Δn=0.035-0.052 Up to vivid 3rd order colors | H(+) nx=1.635-1.827 ny=1.651-1.869 nz=1.670-1.879 | B(+) or B(-) Orthorhombic | 2Vx=46°-98° | In mafic and ultramafic rocks: basalt, dacite, dunite, gabbro, peridotite, pyroxenite In volcanic rocks. Fayalite in syenite, nepheline syenite, phonolite, trachyte, andesine, dacite Forsterite in metamorphosed dolomite. Altered to iddingsite, serpentine (chrysotile, lizardite, antigorite). |
| OMPHACITE (Ca,Na)(Mg,Fe++,Fe+++,Al)Si2O6 (Inosilicate, sodic-calcic clinopyroxene) | Colorless to pale green. Weak Pl. X= colorless, Y= very pale green, Z= very pale green, blue green | Stubby prismatic, 4 or 8 sided sections | Basal section: cleavages intersect at ~87° // to {110} parting // {100} | Simple and lamellar on {100} | Ext. basal: symmetrical // (100): // // (010): 34°-48° Length slow // c | Δn=0.012-0.028Upper 1st order, lower 2nd order | H(+) nx=1.662-1.701 ny=1.670-1.712 nz=1.685-1.723 | B(+) Monoclinic | 2Vz=56°-84° | In eclogite with garnet, plagioclase, quartz, orthopyroxene, kyanite, Fe-Ti oxides. Also in glaucophane schist, amphibolite. Altered to fibrous amphibole |
| OPAL SiO2.nH2O (Oxide, Quartz group) | Colorless, grey, brown. | Colloform. | None | M(-) n=1.43-1.46 R.I. decreases when H2O increases | Isotropic Amorphous | Volcanic. Plutonic. Hydrothermal, Sedimentary. Replaced by quartz, chalcedony. | ||||
| ORTHOCLASE KAlSi3O8 (Tectosilicate. K feldspar, Or100-Or85) | Colorless, pale greyish. Often turbid. Antiperthite: exsolution of K feldspar in Na plagioclase Perthite: exsolution of Na Plagioclase. | Tabular, prismatic, elongated xls. | {001} perfect. {010} good, intersect at 90° | Simple twin: Carlsbad, Manebach, Baveno. | Inclined 5°-6° to {001} cleavage. Extinction could be 13° in Na cryptoperthites. | Δn=0.005-0.008 low: up to 1st order grey | L(-) nx=1.524-1.526 ny=1.518-1.530 nz=1.521-1.533 | B(-) Monoclinic | 2Vx=40°-~70° | In felsic plutonic rocks. In granite, granodiorite, syenite. Also in metamorphic rocks. Authigenic in sedimentary rocks and hydrothermal veins: monoclinic adularia with rhombic cross section Altered to clay and sericite. |
| ORTHOPYROXENE (Inosilicate. A series in the Pyroxene supergroup Hypersthene, Enstatite, Ferrosilite) (Mg,Fe)SiO3 | Pale green. With weak pinkish to greenish pleochroism. | Stubby prismatic. Basal sections 4 or 8 sided. Longitudinal sections are rectangular | Two good prismatic cleavages parallel to the {210} prism faces that intersect at ~90° (87°-93°) | Rare {010} | Longitudinal sections exhibit one cleavage and // extinction Length slow | Δn=0.007-0.020 Usually up to first order yellow, or lower | M(+) H(+) nx=1.649-1.768 ny=1.653-1.770 nz=1.657-1.788 R.I. increasing with increasing Fe content | B(+) or B(-) | 2Vz=50°-132° | Enstatite (Mg px) is common in mafic intrusive rocks (gabbro, norite). Ferrosilite (Fe px) is found in more siliceous igneous rocks (diorite, syenite). Orthopyroxene is common in high grade regional metamorphic rocks Altered to serpentine, talc or fine grained amphibole (Distinguished from clinopyroxene by: 1) lower birefringence, 2) parallel extinction, 3) pale color, weak pleochroism, 4) most common orthopyroxene is optically negative, and 5) high 2V angle). |
| OXYHORNBLENDE (Na,K)0-1Ca2(Mg,Fe++,Fe+++,Al)5(Si,Al)8O22(O,OH)2 (Basaltic hornblende. Inosilicate, clinoamphibole. Not an IMA mineral) | Brown, reddish brown. Zoning is common. Black iron-oxides rim. Strong Pl. X= pale yellow, yellow, pale brown, greenish yellow, Y= brown, reddish brown, brownish green, Z= dark brown, dark reddish brown, dark green brown | Often euhedral in volcanic rocks, prismatic. | {110} intersects at 56° and 124°. | Simple or lamellar on {100} | Symmetrical (basal section). Inclined in sections // (010): 0°-18° Length slow | Δn=0.018-0.083, masked by the strong color of the mineral. Upper 2nd order, 3rd order, 4th order | H(+) nx=1.65-1.72 ny=1.67-1.78 nz=1.68-1.80 | B(-) Monoclinic | 2Vx=56°-88° r<v weak | In volcanic and shallow intrusive rocks: trachyte, basalt, andesite, latite, dacite, rhyolite. Altered to biotite, chlorite. |
| PARAGONITE NaAl2[]AlSi3O10(OH)2 (Phyllosilicate, a dioctahedral mica) | Colorless | Flakes | {001} perfect | {001} | Ext. // cleavage. Inclined ext. <3°. | Δn=0.029-0.036 Up to upper 2nd order | (M+) nx=1564-1580 ny=1.594-1.609 nz=1.600-1.609 | B(-) Monoclinic | 2Vx=0°-40° r>v moderate | Phengite and paragonite in low grade to high grade metamorphic rocks. Phyllite, schist, gneiss. Quartz veins. |
| PECTOLITE (Inosilicate, Wollastonite group) | Colorless | Acicular, radiating | 2 perfect cleav. {100} and {101} intersect at 95° | ~// {100} rare | Ext. ~//. Length slow. Sections cut // (010): inclined ext 16° | Δn=0.030-0.038 Up to upper 2nd order | (M+) nx=1.592-1.610 ny=1.603-1.615 nz=1.630-1.645 | B(+) Triclinic | 2Vz=50°-63° r>v or r>v | In basalt. With zeolites, calcite, prehnite, datolite. In phonolite. In serpentinites, nepheline syenite. In skarn and Ca-rich metamorphic rocks. |
| PERICLASE MgO (Oxide) | Colorless Pale yellow or brown when high Fe No Pl. | Cubic, anhedral, surrounded with fibrous brucite | Perfect {001} | H(+) n=1.736 Up to 1.756 with high Fe content | Isotropic Cubic | High temperature metamorphosed dolomite. With calcite, forsterite, humite, serpentine, brucite, spinel. Altered to fibrous brucite. | ||||
| PERROUDITE Hg5Ag4S5(I,Br)2Cl2 | Bright red, orange red Strong Pl. X=dark brownish red, Y=yellow, Z=brownish-yellow | Prismatic on [001], flattened on {100}, (010) | Perfect {100} | May be contact-twinned with composition plane 0hl | Δn=2.30 | H(+) nα=2.300 nβ=2.400 | B(+) Orthorhombic | 2V=70° (measured) r>v, very strong | Secondary supergene mineral. With Tennantite, Iltisite, Capgaronnite. With Silver halides. Photosensitive | |
| PHLOGOPITE KMg3AlSi3O10(OH)2 (Phyllosilicate dioctahedral mica. A series name in the mica group) | Colorless, pale brown Color zoning Pl. X= colorless, pale yellow, light brown, greenish brown, pale green, Y=Z= brown, olive brown, dark green, dark red brown | Bladed, flakes, hexagonal | {001} perfect | {001}, {110} | Ext. // Length slow | Δn=0.028-0.049 2nd order to 3rd order. | L(-) L(+) M(+) nx=1.53-1.59 ny=1.56-1.64 nz=1.56-1.64 | B(-) Monoclinic | 2Vx=0°-15° v>r | In metamorphosed carbonates, marble, peridotite, lamprophyre, volcanic leucite bearing rocks. |
| PIEMONTITE Ca2(Al,Mn+++,Fe+++)3Si3O11O(OH) (Sorosilicate. Epidote group) (There is also Piemontite-Pb, Piemontite-Sr) | Reddish Distinct Pl. X=yellow, orange, pink, Y=violet, red, Z=deep red, brownish red, pink Color zoning. | prismatic, columnar, bladed, elongated, acicular. Rectangular or 6-sided sections. | {001} perfect | Lamellar {100} rare | Ext. in (010) 13°-32° from trace of cleavage. Length fast or length slow (Thulite ext. is //) | Δn=0.025-0.073 Δn increases with Fe 3rd order, 4th order | H(+) nx=1.730-1.794 ny=1.740-1.807 nz=1.762-1.829 | B(+) or B(-) Monoclinic | 2Vz=64°-106° r>v, also r<v | Low to medium grade regional metamorphic rocks: phyllite, chlorite schist, glaucophane schist. Hydrothermal Mn deposits. |
| PIGEONITE (Mg,Fe++,Ca)(Mg,Fe++)Si2O6 (Inosilicate, clinopyroxene) | Colorless, pale brownish or yellowish green Rare weak Pl. X= colorless, pale greenish brown, pale greenish yellow, Y= pale brown, greenish brown, Z= colorless, pale yellow, pale green | Prismatic. Basal sections 6 or 8 sides, showing cleavages | Good // {110}, intersect at ~ 88° Parting on {010} and {001}. | Simple or lamellar // {100} or {001}. Possible herring bone pattern. | Symmetrical (basal section) Inclined 32°-44° in sections // (010) | Δn=0.023-0.029 1st order yellow and red, up to lower 2nd order | H(+) nx=1.682-1.732 ny=1.684-1.732 nz=1.705-1.757 | B(+). Rarely U(+) Monoclinic | 2Vz=0-32° r>v or r<v weak | Volcanic. Andesites. With augite, hypersthene. In intermediate intrusive rocks. |
| PLAGIOCLASE (Na,Ca)Al(Al,Si)Si2O8 (Tectosilicate. A series name. See Albite, Oligoclase, Andesine, Labradorite, Bytownite, Anorthite) See also MYRMEKITE intergrowths | Colorless. Clouded Pale greyish, reddish, brownish due to inclusions. Zoning. | Tabular // (010). Prismatic elongated | {001} perfect, {010} good, intersect at 93°-94° | Albite // (010) polysynthetic Pericline, Carlsbad | Inclined. Michel-Lévy method or Carlsbad-Albite method Calculate with Ch. de Capitani | Δn=0.007-0.013 1st order grey or white. Anorthite up to 1st order yellow | L(-) L(+) M(+) nx=1.527-1.577 ny=1.531-1.585 nz=1.534-1.590 R.I. increases with anorthite content | B(+) or B(-) Triclinic | 2Vx=45°-102° (high plagioclase) 2Vx=75°-102° (low plagioclase) r<v or r>v | Plutonic, volcanic, metamorphic. Albite: granite, granodiorite, rhyolite, pegmatite, syenite; low grade pelitic metamorphic Oligoclase: granite, granodiorite, rhyolite, pegmatite, syenite; medium, high grade metamorphic. Andesine: diorite, andesite; high grade metamorphic. Labradorite, Bytownite: gabbro, basalt Anorthite: mafic, ultramafic; amphibolite, metamorphosed carbonates |
| PREHNITE Ca2Al2Si3O10(OH)2 (Transitional inosilicate - phyllosilicate structure) | Colorless | Prismatic, tabular, radiating xls, lamellar, bow tie | Basal {001} good | Extinction ~ // Wavy extinction. | Δn=0.022-0.051 Up to middle 2nd order Δn increases with Fe content. 1st order | M(+) H(+) nx=1.611-1.621 ny=1.615-1.637 nz=1.632-1.673 | B(+) Orthorhombic | 2Vz=62°-69° r>v weak r<v strong | Cavities in mafic and volcanic rocks with zeolites, datolite, calcite, pectolite, chlorite, epidote Metamorphic with pumpellyite, lawsonite, albite, epidote, chlorite, zeolites. Found in saussurite. Altered to chlorite, zeolites | |
| PUMPELLYITE Ca2(Al,Fe++,Mg)Al2(SiO4)(Si2O7)(O,OH)2.H2O (Sorosilicate group name) (There is Pumpellyite-Al, -Fe++, -Fe+++, -Mg, -Mn++) | Green, yellow, colorless (Mg-rich) Color zoning related with higher Fe content. Strong Pl. X= colorless, yellow, brownish yellow, greenish yellow, Y= light green, green, blue green, brownish yellow, Z= colorless, yellow, brownish yellow, reddish brown | Prismatic columnar, bladed, acicular xls | {001} good | // or inclined +4° to -34° Length slow (Fe-rich elongated grains) or length fast: | Δn=0.01-0.02 1st order, 2nd order blue. | H(+) nx=1.665-1.711 ny=1.670-1.718 nz=1.683-1.726 | B(+) or B(-) Monoclinic | 2Vz=7°-110° r<v very strong | Metamorphic. In prehnite-pumpellyite facies. In glaucophane schist, with glaucophane, lawsonite, clinozoisite, epidote, chlorite, actinolite, calcite, prehnite. Also in basalt, gabbro. Could alter to chlorite or actinolite. | |
| PYROPHYLLITE Al2Si4O10(OH)2 (Phyllosilicate (Dioctahedral Al-member of the Pyrophyllite - Talc group) | Colorless | Foliated, scales, mica-like, columnar, prismatic, bent xls | {001} perfect | // extinction along trace of cleavage. Length slow | Δn=0.044-0.062 3rd order, 4th order | L(+) M(+) nx=1.552-1.556 ny=1.586-1.589 nz=1.596-1.601 | B(-) Monoclinic and Triclinic | 2Vx=53°-62° r>v | Hydrothermal alteration of Al-minerals: feldspars, andalusite, corundum, kyanite, topaz With quartz, sericite, zoisite, clay minerals | |
| QUARTZ SiO2 (Oxide, Quartz group) See also MYRMEKITE intergrowths | Colorless. Myrmekite: intergrowth quartz and plagioclase. Graphic intergrowth K-feldspar. | Typically anhedral. Prismatic α-Quartz hexagonal prism (low temp.) β- Quartz bipyramid (high temp.) | None. Poor on {101} or {100} ? | Dauphiné, Brazil {110}, Japan {112} | Deformed quartz: undulatory extinction. Length slow. | Δn=0.009 Low: 1st order grey-white, up to cream | L(+) no=1.544 ne=1.553 | U(+) Trigonal | Ubiquitous. Igneous. Metamorphic. Sedimentary. Hydrothermal. | |
| RICHTERITE Na(CaNa)Mg5Si8O22(OH)2 (Inosilicate, clinoamphibole) | Colorless, yellow, violet Pl. variable: pale yellow orange, reddish, violet, blue | Prismatic, Bladed, fibrous | {110} intersects at 56° and 124°. | Simple or lamellar on {100} | Inclined 5°-55° in (010) Length slow. Lower extinction angle for rich Mg content | Δn=0.018-0.025 Upper 1st order, mid 2nd order | M(+) H(+) nx=1.60-1.69 ny=1.61-1.70 nz=1.62-1.71 | B(-) Monoclinic | 2Vx=55°-76° r<v, stronger with Fe content | In metamorphosed limestone, skarn. |
| RIEBECKITE []Na2(Fe++3Fe+++2)Si8O22(OH)2 (Inosilicate, clinoamphibole. Glaucophane - Riebeckite series) (There is also Magnesioriebeckite) | Dark blue. Strong Pl. X= dark blue, Y= reddish blue, grey blue, Z= blue, yellow green, yellow brown | Bladed, prismatic. Fibrous crocidolite. Rhombic basal section | {110} intersects at ~ 55° and 125° | Rare. Simple or lamellar on {100} | Inclined ext. in (010) less than ~22°. Length fast. | Δn=0.006-0.017 Middle to upper 1st order | H(+) nx=1.690-1.702 ny=1.690-1.712 nz=1.702-1.719 | B(-). Or B(+) when Mg rich. Monoclinic | 2Vx=0°-135° r<v strong (+) r>v strong (-) | In alkali granite, syenite, peralkaline rhyolite, trachyte. High pressure metamorphic rocks. |
| RUTILE TiO2 (Oxide) | Reddish, brownish, almost opaque. Pleochroism (yellow, brown-red) > o (yellow, brownish, greenish). Zoning. | Prismatic, elongated, octagonal cross section, acicular | {110} good, {100} distinct | {101}, knee shaped or cyclic twins | //, length slow | Δn=0.286-0.296 High upper order grey, white | VH(+) (extreme) no=2.605-2.613 ne=2.899-2.901 | U(+) Tetragonal | May be anomalously biaxial with 2V=10° | Igneous. With hornblende, biotite. Metamorphic, high temperature metamorphic. Rarely altered to titanite, leucoxene. Polymorph with Anatase and Brookite. |
| SANIDINE high (K,Na)(Si,Al)4O8 (Tectosilicate. K feldspar, Ab0-Ab33) | Colorless, white, yellowish | Phenocryst., radiated, acicular | {001} perfect, {010} distinct | {010} // simple Carlsbad twins | Sections // (010): 20° | Δn=0.005-0.006 Low, 1st order. | L(-) nx=1.518-1.521 ny=1.523-1.525 nz=1.524-1.526 | Monoclinic B(-) | 2Vx=15°-63° r>v weak | Siliceous volcanic rocks. Spherulites in volcanic glasses. Altered to kaolin, sericite, cryptocrystalline silica |
| SANIDINE low (K,Na)(Si,Al)4O8 (Tectosilicate. K feldspar, Ab0-Ab33) | Colorless Zoning | Prismatic, tabular xls. Crosse section: 4 or 6 sided. | {001} perfect. {010} good, intersects at 90° | Carlsbad twins | Sections // to (010): Inclined ext. 5°-9° to {001} cleavage. Sections normal to (010): // extinction to cleavage | Δn=0.004-0.006 Low, 1st order. | L(-) nx=1.518-1.524 ny=1.522-1.529 nz=1.522-1.530 | Monoclinic B(-) | 2Vx=18°-42° | Volcanic: rhyolite, rhyodacite, phonolite, trachyte. With cristobalite. In high temperature metamorphic. Altered to sericite and clay |
| SAPPHIRINE (Mg,Al)8(Al,Si)6O20 (Inosilicate, aenigmatite - sapphirine - surinamite group) | Colorless, blue, pinkish Pl. X= colorless, pale pink, pale yellow, yellowish green, greenish blue, greenish grey, Y= sky blue, pale blue, lavender blue, grey blue, green, Z= blue, reddish blue, blue green, pale green | Tabular, prismatic, ~ elongate | {010} poor | Lamellar twinning on {010} rare | Length slow if xls elongate // c. (010) ext.: 6°-15° | Δn=0.005-0.015 1st order | H(+) nx=1.701-1.731 ny=1.703-1.741 nz=1.705-1.745 | B(-) or B(+) Monoclinic | 2Vx=47°-114° r<v strong | High-grade contact or regional metamorphism With cordierite, kyanite, sillimanite, corundum, spinel, Ca-plagioclase, almandine, orthopyroxene, anthophyllite, hornblende. Usually not with quartz. |
| SCAPOLITE (Tectosilicate group name) (Marialite - Mizzonite . Meionite) | Colorless, cloudy. | Prismatic, bipyramidal prismatic, anhedral. Inclusions: quartz, calcite, feldspar | 2 cleav. // to {110} good 2 cleav. // to {100} distinct Intersect at 45° on basal section | Ext. // Length fast | Δn=0.004-0.038 1st order, 2nd order | L(-) L(+) to M(+) no=1.539-1.600 ne=1.531-1.564 | U(-) Tetragonal | May be biaxial with 2V<10° | Metamorphic. Skarn, marble. With garnet, diopside, actinolite, titanite, calcite, vesuvianite. In amphibolite with hornblende Ca clinopyroxene, epidote, titanite. Also volcanic. Altered to sericite, calcite, chlorite, epidote, zeolites | |
| SERPENTINE group (Mg,Fe++,Ni)3Si2O5(OH)4 (Inosilicate. Chrysotile, Antigorite, Lizardite) | Colorless, pale green Weak Pl: colorless, pale yellow green, pale green. | Prismatic. Fibrous (Chrysotile). Netlike pattern (Lizardite). Foliated (Antigorite) | {001} perfect (antigorite) | Ext. // to the length of fibers (chrysotile) Length slow (antigorite) | Δn=0.001-0.010 1st order grey or white | L(-) L(+) M(+) nx=1.529-1.595 ny=1.530-1.603 nz=1.537-1.604 R.I. increases with Fe content | B(-) Monoclinic. Also triclinic, hexagonal | 2Vx=20°-50° r>v or r<v | Hydrothermal alteration of peridotite, pyroxenite. Produced from alteration of olivine, pyroxene. With magnetite, talc, calcite, brucite, chlorite, chromite. In metamorphosed carbonates. With calcite, forsterite, dolomite, magnesite. Altered to chlorite. | |
| SIDERITE Fe++CO3 (Carbonate, calcite group) | Colorless, grey, pale yellow, brownish Pleochroic o>e | Rhombohedral, botryoidal | {101} perfect | Lamellar on {01-12} rare | Extinction symmetrical or inclined to cleavage traces | Δn=0.240 Very high upper order white | H(+) no=1.875 ne=1.635 | U(-) Hexagonal, Trigonal | In sedimentary iron formations. Gangue mineral in high temperature hydrothermal veins Altered to goethite; also to hematite or magnetite | |
| SILLIMANITE Al2SiO5 (Nesosilicate sillimanite - andalusite - kyanite group) | Usually colorless. Could look greyish due to spray of inclusions. Pale brown (fibrolite). Pl. (colored varieties) X= yellow or colorless pale yellow, Y= green yellow or colorless or pale yellow, Z=colorless or violet brown or blue | Slender prismatic xls, elongated on c, fibrous (fibrolite): Rhombic shaped basal {110}. | {010} good | // extinction Length slow | Δn=0.018-0.022 Up to lower 2nd order. Fibrolite: 1st order yellow. | M(+) H(+) nx=1.653-1.661 ny=1.657-1662 nz=1.672-1.683 | B(+) Orthorhombic | 2Vz=21°-30° r>v strong | In high temperature rocks. Metamorphic. In mica schist, gneiss, hornfels. Also in granite, pegmatite. With kyanite, andalusite, staurolite, muscovite, biotite, feldspar, cordierite, corundum, garnet. Altered to sericite | |
| SODALITE Na8Al6Si6O24Cl2 (Tectosilicate. feldspathoid, sodalite group: sodalite, nosean, haüyne) | Colorless, grey, very pale blue. Dark rim. No pleochroism. | Six sided cross section | Poor {110} | {111} difficult to observe | M(-) n=1.483-1.490 | Isotropic Cubic | Silica deficient alcalic igneous rocks. Volcanic, phonolite, trachyte. Plutonic, nepheline syenite. With nepheline, leucite, sanidine Altered to zeolite (fibrous), clay, calcite, cancrinite | |||
| SPINEL (Mg,Fe++) Al2O4 (Oxide. a group name including spinel series, magnetite series, chromite series. Here: spinel series) | Colorless, pinkish, bluish, greenish grey (spinel), deep green (hercynite) | Octahedral xls. Square, rhombic, triangle cross section. | None. Parting on {111} | Contact plane {111} difficult to observe | VH(+) n=1.719 Spinel n=1.835 Hercynite n=1.805 Gahnite n=1.920 Galaxite | Isotropic Cubic | High grade metamorphic with andalusite, kyanite, sillimanite, corundum, cordierite, orthopyroxene Regional metamorphosed carbonates rocks, with chondrodite, phlogopite, calcite, forsterite In contact metamorphic, granulite. Hercynite, Picotite in ultramafic. Gahnite in granite pegmatite, and hydrothermal. Galaxite with Mn minerals, spessartine, rhodonite. | |||
| SPODUMENE LiAlSi2O6 (Inosilicate, Li clinopyroxene) | Usually colorless. Some gems with green or lilac. Pl. (colored specimens): green, lilac shades | Prismatic, lamellar. Octagonal section. | Basal section: cleavages {110} intersect at ~87. Parting on {010} and {100}. | Twin. on {100} | Basal (2 cleavages): symmetrical ext. Longitudinal // (010): 20°-26° inclined ext. Length slow | Δn=0.014-0.027 Upper 1st order to mid 2nd order | M(+) H(+) nx=1.648-1.668 ny=1.655-1.671 nz=1.662-1.682 | B(+) Monoclinic | 2Vz=58°-68° | In Granitic pegmatite (Li-rich). With quartz, feldspar, beryl, tourmaline, lepidolite. Altered to Li-mica, albite, eucryptite |
| STAUROLITE (Fe++,Mg,Zn)2Al9(Si,Al)4O22(OH)2 (Nesosilicate) (There is also Magnesiostaurolite, Zincstaurolite) | Pale yellow, honey yellow, yellow brown. Color zoning. Distinct Pl. X= colorless, pale yellow, Y= pale yellow, yellowish brown, Z= golden yellow, reddish brown | Prismatic xls. Rhombic shape. Twins. Inclusions. | {010} poor | Penetration twins {031}: 90° Brittany cross. Penetration twins {231}: 60° St Andrew cross. Contact {031} rare | // extinction (longitudinal). Symmetrical (basal) Length slow | Δn=0.011-0.014 Up to 1st order white, yellow | H(+) nx=1.736-1.747 ny=1.742-1.754 nz=1.748-1.761 | B(+) Monoclinic, pseudo-orthorhombic | 2Vz=80°-90° 2V decreases when Fe increases. r>v weak to moderate | Medium grade regional metamorphic. Mica schist. With garnet, muscovite, biotite, andalusite, sillimanite, kyanite, chloritoid, cordierite, chlorite. |
| STILBITE (Ca0,5,Na,K)9[Al9Si27O72].28H2O (Tectosilicate, zeolite, heulandite - stilbite - brewsterite group) (There is Stilbite-Ca, Stilbite-Na) | Colorless | Tabular,radiating bundles of xls, bow tie | {010} good | {100} cruciform penetration twins | ~ inclined, ~ // ext. to (010) Length fast or length slow | Δn=0.006-0.014 1st order | L(-) M(-) nx=1.484-1.500 ny=1.492-1.507 nz=1.494-1.513 | B(-) Monoclinic | 2Vx=30°-49° r<v | In lacustrine sediments. In basalt, gabbro, serpentinite. Volcanic altered rocks Altered to clay, zeolites |
| STILPNOMELANE K(Fe++,Mg,Fe+++,Al)8(Si,Al)12(O,OH)27.2H2O (Phyllosilicate) | Pale yellow, brown, dark brown, green Basal sections are dark Pl. X= pale yellow, golden yellow, Y=Z= brown, reddish brown, greenish brown, black | Bladed, elongated, thin prismatic, sheaflike aggregates | {001} and {010} intersect at 90° Basal cleav. less perfect than in biotite. | Trace of basal cleavage // and length slow (no or poor bird-eye ext.) | Δn=0.030-0.110 Upper 2nd order, 3rd order, High upper order 4th order, creamy 5th order and 6th order | L(+) M(+) H(+) nx=1.543-1.634 ny=1.576-1.745 nz=1.576-1.745 R.I. increases with Fe | B(-), appears U(-) Triclinic (pseudomonoclinic) Sections cut to (001) appear isotropic | 2Vx=~0° | Low grade regional metamorphism. With chlorite, muscovite, garnet, amphibole, glaucophane, calcite, epidote group, pumpellyite. In metamorphosed iron formations. Altered to clay, chlorite, iron oxides | |
| TALC Mg3Si4O10(OH)2 (Phyllosilicate (Pyrophyllite - Talc group) | Colorless Weak Pl. colorless, pale yellow green, pale green | Flakes, foliated | {001} perfect | // extinction Length slow | Δn=0.05 3rd order | L(+) M(+) nx=1.539-1.550 ny=1.589-1.594 nz=1.589-1.600 R.I. increases with Fe | B(-) Triclinic | 2Vx=0°-30° r>v weak to moderate | Hydrothermal altered mafic and ultramafic: With serpentine, magnesite. Metamorphic. Blue schist with glaucophane. Mica schist. Talc schist, with magnetite, tremolite, chlorite, anthophyllite, serpentine. In metamorphosed dolomite with calcite, dolomite, tremolite. | |
| THOMSONITE Ca2Na[Al5Si5O20].6H2O (Tectosilicate, zeolite, natrolite group) | Colorless | Prismatic, columnar, fibrous, radiating aggregates | {010} perfect and {100} intersect at 90° | {110} rare | Ext. // Length slow | Δn=0.006-0.021 1st order grey to yellow | L(-) nx=1.497-1.530 ny=1.513-1.533 nz=1.518-1.544 | B(+) Orthorhombic, pseudotetragonal | 2Vz=42°-75° | In lacustrine sediments. In basalt, gabbro, serpentinite. Volcanic altered rocks. |
| THULITE Ca2Al3[Si2O7][SiO4]O(OH) (Sorosilicate, a pink variety of orthozoisite with up to 2% of Mn) | Colorless to pleochroic. X= deep pink, Y= pale pink, Z= pale yellow, yellow | Prismatic, columnar, bladed, anhedral | Perfect // {100} | // extinction in (010) | Δn=0.006-0.018 1st order, 2nd order Slightly anomalous since superposition of color to birefringence. | H(+) nx ~1.700 ny ~1.703 nz ~1.708 (thulite frpm Øvstebø) | B(+) Orthorhombic | 2Vz ~71°, variable due to chemical zoning (thulite from Øvstebø) | In pegmatite and hydrothermal veins. | |
| TITANITE CaTiSiO5 (Nesosilicate) | Brown. Rarely yellow or colorless. Weak Pl. X= colorless, pale yellow, Y= yellow brown, pink, greenish yellow, Z= orange brown, greenish brown, green, red | Prismatic rhombic shaped xls | Good prismatic {110} | Simple twins {100} Lamellar {221} | Inclined 36° to 51° to the trace of cleavage. Rhombic sections: symmetrical ext. Length fast | Δn=0.100-0.192 Extreme. High upper order grey. | H(+) VH(+) nx=1.843-1.950 ny=1.870-2.034 nz=1.943-2.110 | B(+) Monoclinic | 2Vz=17°-40° r>v very strong | Igneous, syenite, monzonite, granodiorite, diorite. With biotite, hornblende. Metamorphic, glaucophane schist, mica schist, amphibolite, gneiss, skarn, marble. Volcanic: phonolite. Altered to leucoxene. |
| TOPAZ Al2SiO4(F,OH)2 (Nesosilicate) | Colorless Pl. X=Y= ~yellow, Z= ~pink | Prismatic. Square or rhombic basal section | {001} perfect | // ext. in longitudinal sections Symmetrical on rhombic section. Length fast on cleavage. Length slow on elongation. | Δn=0.008-0.011 1st order white or pale yellow | M(+) nx=1.606-1.634 ny=1.609-1.637 nz=1.616-1.644 | B(+) Orthorhombic | 2Vz=48°-68° r>v | Plutonic, volcanic rocks. In rhyolite. Hydrothermal with W, Sn, Mo, Au. metamorphic quartzites, schists. With muscovite. Altered to sericite, clay. | |
| TOURMALINE Na(Mg,Fe,Li,Al)3Al6(Si6O18)(BO3)3(OH,F)4 (Cyclosilicate group name: Schorl, Dravite, Elbaite, etc.) Schorl NaFe3Al6(Si6O18)(BO3)3(OH)4 Dravite NaMg3Al6(Si6O18)(BO3)3(OH)4 Elbaite Na(Li,Al)3Al6(Si6O18)(BO3)3(OH)4 | Variable, grey, blue, green, pink, colorless. Concentric zoning. Strong pleochroism o>e e= grey, green, blue, yellow, brown, pink; o= colorless, light colored | Prismatic. Acicular. Hexagonal, rounded triangular cross section | Poor {110} {101} Fractures perpendicular to xl length | Rare {101} | // extinction in longitudinal section. Length fast. | Δn=0.017-0.035 1st order, 2nd order | M(+) H(+) no=1.63-1.70 ne=1.61-1.68 R.I. increases with Fe | U(-) Hexagonal Trigonal | Occasionally biaxial with 2V~10° | Granitic pegmatite, granite, granodiorite. Metamorphic, schist, gneiss, phyllite. Hydrothermal. Also in greisen. Altered to sericite, chlorite, lepidolite, talc. |
| TREMOLITE []Ca2Mg5Si8O22(OH)2 (Inosilicate. Clinoamphibole, Tremolite - Actinolite - Ferro-actinolite series.) | Colorless Weak green Pl. | Prismatic columnar, bladed, acicular, fibrous. Rhombic basal section. | {110} intersects at 56° and 124°. Visible on basal sections | Simple or {100} lamellar, // to the long diagonal of basal section | Inclined section (010): 17°-21°. Sections // to (100) show // extinction Length slow. | Δn=0.022-0.027. Up to mid 2nd order. | M(+) nx=1.600-1.620 ny=1.612-1.630 nz=1.625-1.645 R.I. increases with increasing Fe content. | B(-) Monoclinic | 2Vx=84°-88° r<v weak | Low grade and contact metamorphic metamorphic limestone. With calcite, dolomite, forsterite, garnet, diopside, wollastonite, talc, epidote. Also in mafic and ultramafic rocks. In blue schists. Altered to chlorite, talc, carbonates. |
| TRIDYMITE (β-TRIDYMITE) SiO2 (Oxide, Quartz group) | Colorless | Hexagonal, anhedral | Poor prismatic cleavage. Often none. | {106} | Elongated xls // ext. Length fast | Δn=0.002-0.004 | M(-) nx=1.471-1.479 ny=1.472-1.480 nz=1.474-1.483 | B(+) Orthorhombic (pseudohexagonal) | 2V=40°-90° | Volcanic. Plutonic. In basalt with quartz, cristobalite, fayalite, sanidine, topaz, hematite, garnet. β-Tridymite alters to α-Tridymite. |
| VESUVIANITE Ca10Mg2Al4(SiO4)5(Si2O7)2(OH)4 (Sorosilicate) | Colorless. Pale yellow, brown, green Anomalous interference colors. Weak Pl. o>e | Stubby tetragonal prismatic, anhedral | Poor {110} | Elongate xls: length fast. Ext. // | Δn=0.001-0.020 Low 1st order, middle 1st order | H(+) no=1.702-1.795 ne=1.700-1.775 | U(-) or U(+) Tetragonal | Contact metamorphic limestone. With garnet, grossular, diopside, wollastonite, tremolite, calcite, epidote. In nepheline syenite. In altered gabbro, peridotite. | ||
| WINCHITE []{CaNa}{Mg4Al}(Si8O22)(OH)2 (Inosilicate, Amphibole group, winchite subgroup) | Monoclinic | |||||||||
| WOLLASTONITE CaSiO3 (Inosilicate, wollastonite group) | Colorless | Prismatic, columnar, bladed, fibrous | {100} perfect. {001} and {-102} intersect at 84.5°. {-102} and {100} intersect at 70° | {100} | // ext. in section (100) Other sections are inclined. Length slow. | Δn=0.013-0.017 1st order yellow | M(+) nx=1.616-1.645 ny=1.628-1.652 nz=1.631-1.656 | B(-) Triclinic | 2Vx=36°-60° | In metamorphic limestone and dolomite. With calcite, dolomite, tremolite, epidote, grossular, augite, monticellite, forsterite |
| XENOTIME YPO4 (Phosphate) | Colorless, yellow, pale brown Weak Pl. o= pale pink, yellow brown, yellow, e= pale brownish yellow, greyish brown, greenish | Prismatic, tetragonal, elongate, radial aggregates | {100} | Simple on {101} elbow shaped twins | // ext. Length slow | Δn=0.070-0.107 High upper order | H(+) no=1.690-1.724 ne=1.760-1.827 | U(+) Tetragonal | Plutonic. Granite, syenite, granodiorite, pegmatite. Metamorphic, in mica schist, gneiss, marble | |
| ZIRCON (Zr,Hf)SiO4 (Nesosilicate) | Colorless, pinkish, pale brown, yellow Weak Pl. o<e | Stubby prismatic, anhedral. Tetragonal xls with pyramidal terminations | Poor {110} and {111} | {111} rare | Longitudinal sections show // extinction Length slow | Δn=0.042-0.065. High upper order. Up to 3rd order, 4th order | H(+) VH(+) no=1.923-1.960 ne=1.961-2.015 | U(+) Tetragonal | Anomalous 2V=0°-10° | Plutonic felsic rocks. In granite, syenite, granodiorite, pegmatite. Metamorphic: in mica schist, gneiss, schist. Inclusion with halo in biotite, cordierite, chlorite, tourmaline With quartz, feldspar, biotite, hornblende. |
| ZOISITE Ca2Al3[Si2O7][SiO4]O(OH) (Sorosilicate) | Colorless, grey, grey-green. XPL: anomalous blue interference colors unevenly distributed. Pl. (Thulite) X= pink, Y= pale pink, colorless, Z= pale yellow, pink zones | Prismatic, columnar, bladed, acicular, anhedral | Perfect // {100} | // extinction in (010). Length fast:zoisite Length slow: Fe-rich zoisite Both elongations in zoned xls | Δn=0.003-0.020 1st order, 2nd order | H(+) nx=1.685-1.705 ny=1.688-1.710 nz=1.698-1.725 R.I. increases with Fe content | B(+) Ferrian zoisite Also B(-) Orthorhombic | 2Vz=0°-50° (> 60° with Fe) r>v (zoisite) r<v (ferrian zoisite) | Low grade to medium grade metamorphic: schist, gneiss, marble With Na plagioclase, garnet, biotite, hornblende, muscovite, calcite |
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Liber Liber 2023 -
Authors
abati
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