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.

USE (see picture)

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.

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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 (Inosilicate. A supergroup name. Orthorhombic amph.: Anthophyllite, Holmquistite, Ferrogedrite, etc. Monoclinic amph.: Cummingtonite, Grunerite. Tremolite, Actinolite. Hornblende. Glaucophane, Riebeckite. Katophorite. Arfvedsonite. Richterite, Pargasite, Winchite, etc.) General formula: A0-1B2C5T8O22W2 A=Na,K,Ca,Li,[] (vacancy) B=Na,Ca,Fe++,Mg,Mn++,Li C=Mg,Fe++,Mn++,Al, Fe+++,Mn+++,Ti++++,Li T=Si,Al,Ti++++ W=(OH),F,Cl,O--	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

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Bibliography

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