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Properties in bold are particularly distinct for that mineral. Click on the icon next to the mineral to swipe through pictures.
| Mineral | Colour | Birefringence | Relief | Noteworthy Features | Cleavage | Extinction | Habit | 2V Angle | Optic Sign | Found In | Associated Minerals | Mineral Group | Crystal System |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Actinolite | Colourless to Green Pleochroic. More Green for more Fe-rich | Moderate. 0.027 up to mid 2nd order | Moderate | C to Epidote: less Yellowish and lower relief / Length Slow | Good. 2 sets at 124° | Inclined 30° max / Typically 15° | Fine Prisms / Laths / Fibrous / Needle-like | Large 75-80° | Negative | Metamorphic (Green and Blueschist, Serpentinite, Marbles) | Actinolite Amphibole | Monoclinic | |
| Aegirine | Bright Green / Yellow / Brown / Pleochroic | High. 0.04-0.06 up to 3rd or 4th | High | May occur as rim on other green pyroxenes / Length Fast | Good. 2 sets at 87° | Inclined 0-10° | Needle Prisms / Hexagonal | Large 80-90° | Negative | Igneous | Albite Epidote Biotite Sphene Talc Calcite Chlorite Quartz Sericite | Clinopyroxene | Monoclinic |
| Aenigmatite | Dark Brown to opaque / Strongly Pleochroic in very thin sections | Very High | High to Very High | Intergrowths with Arfvedsonite are common / Opaque to smoky haloes around Orthite inclusions / Polysynthetic Twinning | Good. 2 sets at 66° | Inclined 4-45° | Columns / Needles | Small to Moderate 27-55° | Positive | Igneous (Felsic, Na-rich rocks) | Anorthoclase Arfvedsonite Clinopyroxenes Nepheline | Sapphirine Supergroup | Triclinic |
| Akermanite | Colourless / Weakly Pleochroic | Low | Moderate | May have anomalous interference colours (Purple Blue) / Interpenetrating twinning / Length Fast | Poor. 2 sets | Straight | Plates | Uniaxial | Positive | Igneous (Silica-undersaturated Volcanic rocks) / Metamorphic | Epidote Sphene Tourmaline | Melilite | Tetragonal |
| Albite | Colourless | Low. up to cream | Very Low | Albite Twinning lengthways / Carlsbad Twinning / Common in low-grade Metamorphic rocks with Chlorite, Muscovite and Actinolite / May occur as rims on more calcic plagioclase later replacement of feldspars in Igneous rocks. | Perfect and Good. 2 sets at 86° | Inclined 12-20° | Prisms | Large 70-80° | Positive | Igenous / Metamorphic | Leucite Nepheline Olivine Titanaugite | Plagioclase Feldspar | Triclinic |
| Allanite / Orthite | Yellow / Pink / Magenta / Deep Brown Pleochroism | Moderate to High. 0.018-0.030 | High | Commonly zoned / with Epidote and Clinozoisite rims (due to radiation damage) / Rich in REE | Poor | Straight or Inclined | Irregular Prisms / Needles | Moderate to Large 40-80° | Negative | Igneous (Acid to Intermediate rocks) / Metamorphic (Low to High grade regional metamorphism) | Biotite Cordierite Quartz Sericite Muscovite | Epidote | Monoclinic |
| Almandine | Colourless / Reddish | Isotropic | High | Porous texture / Heliocentric inclusion spirals | None | Isotropic | Euhedral (Rhombic Dodecahedrons; like a Hexagon with more faces) / Anhedral Grains | Isotropic | Isotropic | Metamorphic (Low to high grade) | Biotite Clinopyroxene Olivine Hornblende MicroclineK-Feldspar Orthopyroxene Quartz Titanaugite Volcanic Glass | Garnet | Cubic |
| Analcime / Analcite | Colourless | Very Weak (may be anomalous) | Low | Often in groundmass between Plagioclase grains in Dolerite and Basalt rocks / Replaces Leucite / Polysynthetic Twinning | Poor | Almost Isotropic | Euhedral / Anhedral / usually deformed / Spheres | Nearly Isotropic | Negative | Igenous (Basic volcanic rocks) | Biotite Clinopyroxene Olivine Hornblende MicroclineK-Feldspar Orthopyroxene Quartz Titanaugite Volcanic Glass | Zeolite | Triclinic / Pseudo Cubic |
| Anatase | Yellow Brownish / Blue / Opaque | Very High | Very High | May have zoned colour distribution / Length Fast | Perfect. 2 sets | Straight | Detrital / Granular / Needles | Uniaxial | Negative | Sedimentary | Oxide | Tetragonal | |
| Andalusite | Colourless / Red / Yellow / Green / Pale Pink Pleochroic | Low. 0.009-0.012 up to White | Moderate | May alter to Mica / Patchy Pink colouration / Graphite inclusions / Length Fast | Good | Straight | Prisms / Cubes / Needles | Large 70-90° | Negative | Metamorphic (Low-P metapelites) / rare in igneous | Al Silicate | Orthorhombic | |
| Andesine | Colourless | Low. up to pale Gray | Very Low | Albite Twinning lengthways / Carlsbad Twinning / Often zoned / with Hornblende in Igneous rocks / Found in medium to high grade metamorphic rocks | Perfect and Good. 2 sets at 86° | Inclined 12-28° | Prisms / Tabular / Laths | Large 70-90° | Negative | Igenous / Metamorphic (Medium to High grade) | Calcite Zeolite | Plagioclase Feldspar | Triclinic |
| Andradite | Green to Brown | Isotropic (may be anomalous) | Very High | Zonal growth rings / Mottled colour texture | None | Isotropic | Euhedral (Rhombic Dodecahedrons; like a Hexagon with more faces) / Anhedral Grains | Isotropic | Isotropic | Metamorphic (Fe-metasomatosed skarn) | Biotite Diopside Hornblende Hypersthene Olivine Plagioclase | Garnet | Cubic |
| Anhydrite | Colourless | Very Low | Very High to Moderate | Distorted cleavage planes / Alters to Gypsum with water / Polysynthetic Twinning | Good. 3 sets | Straight | Granular / Needles | Moderate to Small 42° | Positive | Sedimentary (Evaporites) | Albite Almandine Chlorite Clinopyroxene Hornblende Kyanite MuscoviteK-Feldspar Orthopyroxene Plagioclase Quartz Staurolite Volcanic Glass | Sulphate | Orthorhombic |
| Anorthite | Colourless | Low. up to cream / Yellow | Low | Distinctive Twinning lengthways / Often zoned: typically Anorthite (Ca-rich) centres and Albite (Na-rich) rims. Anorthite cores tend to alter to a fine-grained, turbid, white mica (Sericite) / More commonly found in very high grade metamorphic rocks than in igneous rocks | Perfect and Good. 2 sets at 86° | Inclined 52° | Prisms | Large 80-90° | Negative | Igneous / Metamorphic (High grade) | Biotite Clinopyroxene Olivine Hornblende MicroclineK-Feldspar Orthopyroxene Quartz Titanaugite Volcanic Glass | Plagioclase Feldspar | Triclinic |
| Anorthoclase | Colourless | Very Low | Very Low to Low | Cross Hatched twinning / Length Fast | Good. 2 sets at 90° | Plates / Lath-Like / Granular | Moderate to Large 60-110° | Positive / Negative | Igneous (Na-rich Volcanic rocks) | Alkali Feldspar | Monoclinic | ||
| Anthophyllite | Colourless | Low to Moderate. 0.013 up to mid 2nd order | Moderate | Occurs in Mg-rich metamorphic rocks (e.g. low-grade metabasites) / Often with Talc / Like Actinolite but parallel extinction / Length Slow | Good. 2 sets at 124° (Amphibole Cleavage) | Straight | Prisms | Large 70-90° | Positive | Metamorphic (Low-P metapelites) | Aegirine-Augite Calcite Melanite Nepheline Sanidine Sodalites | Amphibole | Orthorhombic |
| Antigorite | Colourless to Pale Green / Weakly Pleochroic | Very High | Low to Moderate | Fan-shaped multiple twins with undulose extinction / Grid texture in ultrabasic rocks / Length Slow | Perfect | Straight / May be Undulose | Radiating / Flaky / Long Prisms / Scaly | Small to Moderate 27-60° | Negative | Metamorphic (Low grade and Serpentinites) | Serpentine | Monoclinic | |
| Apatite | Colourless / Pale Red Grey or Brownish | Very Low. 0.002 Gray | Moderate | Usually as tiny elongate crystals with rounded or hexagonal outline / Often as accessory mineral / Length Fast | Poor. 2 sets | Straight | Hexagonal / Elongate Prisms / Laths / Oolitic spheres / Radiating branches | Uniaxial | Negative | Igneous / Metamorphic / Sedimentary | Albite Almandine Biotite Chlorite Quartz Rutile Sericite | Phosphate | Hexagonal |
| Apophyllite | Colourless | Very Low | Low | Perfect | Straight | Platy / Granular / Tabular | Uniaxial | Positive / Negative | Igneous (Fractures and Amygdules in basic Volcanic rocks) | Olivine Serpentine Titanaugite | Tetragonal | ||
| Aragonite | Colourless | Very High. 0.155 | Low to High | No rhombohedral Cleavage / Simple to Lamellar twinning / Length Fast / Cavity Filling in volcanic rocks | Poor | Straight | Prisms / Radiating needles | Small 18° | Negative | Sedimentary (with organics) | Carbonate | Orthorhombic | |
| Arfvedsonite | Green / Purple / Brown / Dark Blue / Pleochroic | Very High / May be Anomalous | Moderate to High | Poikilitic sieve texture / Simple Twinning / Length Fast | Perfect and Good. 2 sets | Inclined 65-80° | Thick Columns / Elongate Prisms / Needles / Granular / Flaky | Small to Large 0-100° | Positive / Negative | Igneous (Nepheline Syenite) | Andalusite Biotite Garnet Hercynite Hypersthene Quartz K-Feldspar Muscovite Plagioclase Quartz Sillimanite | Alkali Amphibole | Monoclinic |
| Augite Group | Colourless to Pale Green / Brown / Pleochroic | Moderate. 0.018 | Moderate to High | Simple Twinning / May have zoned colour distribution / Relief changes depending on orientation / Alters to Amphibole, Chlorite, Epidote and Talc / Replaces Diopside in Limestones | Good. 2 sets at 87° | Inclined 35-50° / May be Undulose | Prisms / Hexagonal / Needles | Moderate 60° | Positive | Igneous (Alkaline basalts) / Metamorphic | Almandine Also Garnet Clinozoisite Epidote Jadeite Lawsonite Omphacite Pumpellyite Rutile Zoisite | Clinopyroxene | Monoclinic |
| Barite | Colourless | Very High | Moderate | Kinking and crenulation / Polysynthetic Twinning / Length Fast | Good. 3 sets | Straight | Flaky / Granular / Fibrous / Columns / Elongate Prisms / Platy / Radial | Moderate 36-38° | Positive | Igneous / Metamorphic / Sedimentary (as gangue in hydrothermal deposits, in concretions in sandstone and in desert roses) | Orthorhombic | ||
| Barrosite Group | Blue Green / Pleochroic | Very High | Moderate to High | May have pleochroic haloes / Use associated minerals to distinguish from other amphiboles / Alters to Actinolite, Antigorite, Chlorite / Length Slow | Perfect. 2 sets at 124° | Inclined 15-22° | Short to Long Columns / Elongate Prisms / Needles | Moderate to Large 65-90° | Negative | Metamorphic (Low grade) | Augite Olivine Pigeonite Plagioclase | Green Hornblende Amphibole | Monoclinic |
| Beryl | Colourless / Pale Blue to Pale Green / Weakly Pleochroic | Low | Very High to Moderate | May be anomalously Biaxial / Length Fast | Poor | Straight | Short to Long Prisms / Granular | Uniaxial | Negative | Igneous (Granite pegmatites) / Metamorphic | Hexagonal | ||
| Biotite | Brown or Green / Pleochroic | High. 0.028 | Moderate to High | Easily altered to Chlorites or Clays / More opaque in volcanic rocks / Mottled / Length Slow | Perfect | Straight or Inclined 5° | Hexagonal / Plates | Small 0-35° | Negative | Igneous / Metamorphic | Biotite Mica | Monoclinic | |
| Bronzite | Pale Green / Weakly Pleochroic | Very High | Moderate to High | A variety of Enstatite / Zoning with Mg-rich core in Colcanic rocks / often with exsolution lamellae in Plutonic rocks / Alters to serpentine | Good. 2 sets | Short Columns / Elongate Prisms / Granular | Large to Moderate 97-63° | Positive / Negative | Igneous (Basic to ultrabasic rocks) | Hematite Quartz Topaz Tourmaline | Orthopyroxene | Orthorhombic | |
| Bytownite | Colourless | Low. up to cream | Low | Albite Twinning lengthways / Carlsbad Twinning / Often zoned: typically Anorthite (Na-rich) centres and Albite (Ca-rich) rims. Anorthite cores tend to alter to a fine-grained, turbid, white mica (Sericite) / Often with Clinopyroxene and/or Olivine in Igenous rocks. | Perfect and Good. 2 sets at 86° | Inclined 40-52° | Rectangular Laths / Prisms | Large 80-90° | Negative | Igenous / Metamorphic (High grade) | Plagioclase Feldspar | Triclinic | |
| Calcite | Colourless | Very High. 0.172 Extreme pastel colours | Low to High | Twinkling Cleavage / Lamellar Twinning / Found infilling Fauna and Flora in carbonates / Length Fast | Perfect. 3 sets (Rhombohedral) | Straight | Interlocked Grains / Fibrous / Oolitic spheres | Uniaxial | Negative | Metamorphic / Sedimentary | Carbonate | Trigonal | |
| Cancrinite | Colourless / Pale Yellow | Moderate. 0.018 | Low Negative | Often replaces Nepheline / Length Fast | Perfect | Straight | Elongate Prisms / Laths / Fibrous | Uniaxial | Negative | Igneous | Almandine Also Garnet Clinozoisite Epidote Jadeite Lawsonite Omphacite Pumpellyite Rutile Zoisite | Feldspathoid | Hexagonal |
| Carbon (Organic) | Brownish to Gray / Opaque | Very Low to Very High | As a black pigment in many organic rich rocks | Not a crystal | Granular (Small) | Not a crystal | Not a crystal | Metamorphic (Low-grade) / Sedimentary (Organic rich) | Amorphous | ||||
| Cassiterite | Gray / Yellow / Red / Brown / Weakly Pleochroic | Very High | Very High | May have zoned colour distribution / Pleochroic haloes / Twinning / Length Slow | Good | Straight | Granular / Prisms / Needles | Uniaxial | Positive | Igneous (Pegmatitic Ore deposits) / Metamorphic (Greisen and contact skarn) | Clinopyroxenes Leucite Melanite Nepheline Olivine Plagioclase Volcanic Glass Sanidine Titanaugite | Tetragonal | |
| Celadonite | Green / Pleochroic | Very High | Moderate | Pseudomorphs after Olivines / Length Slow | Pefect | Inclined 2-3° | Radiating / Fine Grained | Small 0-20° | Negative | Igneous (Cavity filling in basalts) / Metamorphic (Zeolite facies) | Monoclinic | ||
| Chabazite | Colourless | Very Low to Low | Very Low | Mostly as subgrains / Simple Twinning | Good | Straight | Cubes / Prismatic | Small 0-30° | Positive / Negative | Igneous (Cavity and Fractures Filling in Volcanic rocks, in veins in plutonic rocks) | Cubic Zeolite | Trigonal | |
| Chalcedony | Colourless | Low | Very Low to Low | Straight | Needles / Radiating / Dense | Uniaxial | Positive | Igneous (Fractures and Amygdules in Volcanic rocks) | Chromite Hematite Magnetite Pentlandite Pyrite Pyrrhotite Rutile Tantalite | Framework SiO2 | Trigonal | ||
| Chlorite Group | Colourless / Green | Low or Very low. up to Gray. Usually anomalous blue, purple, | Moderate | Often with Muscovite / Also as alteration product (often of biotite) | Perfect | Inclined 0-10° | Hexagonal / Plates | Small | Positive or Negative | Low-grade Metamorphic | Biotite Clinopyroxene Olivine Hornblende MicroclineK-Feldspar Orthopyroxene Quartz Titanaugite Volcanic Glass | Sheet | Monoclinic |
| Chlorite (Fe2+) | Dark Olive Green to Brown-Green / Pleochroic | Very High / May be Anomalous Blue | Moderate to High | Length Slow | Perfect | Straight (Parallel to Cleavage) | Thin to Thick Plates / Flaky / Scaly / Fibrous | Small 0-30° | Negative | Metamorphic (Low grade and Blueschist facies) | Epidote Glaucophane Lawsonite Pumpellyite | Orthochlorite Chlorite | Monoclinic |
| Chlorite (Mg, Fe2+) | Pale Green / Weakly Pleochroic | Very High / May be Anomalous Blue or Brown | Moderate | Perfect | Straight (Parallel to Cleavage) | Thin to Thick Plates / Flaky / Scaly / Fibrous | Small to Moderate 0-10° (if Positive) / 0-40° (if Negative) | Positive / Negative | Igneous (Amygdules in magmatic rocks) | Orthochlorite Chlorite | Monoclinic | ||
| Chlorite (Mg) | Colourless / Greenish / Weakly Pleochroic | Very High / May be Anomalous Blue | Very High to Moderate | Anomalous birefringence for Pennine, normal for Clinochlore | Perfect | Straight (Parallel to Cleavage) | Thin to Thick Plates / Flaky / Scaly / Fibrous | Small 0-30° (if Positive) / 0-5° (if Negative) | Positive / Negative | Igneous (Ultrabasic rocks, palaeo-rhyolites and acidic plutonic rocks) | Almandine Biotite K-Feldspar Muscovite Plagioclase Quartz Staurolite | Orthochlorite Chlorite | Monoclinic |
| Chloritoid | Colourless / Green or Gray Blue Pleochroic | Low | High | Cleavage not as good as Mica / Twinning / Hourglass texture | Perfect. 2 sets | Almost Straight | Prisms / Euhedral / Spherical | Moderate 36-70° | Positive | Metamorphic (Low Grade) | Albite Glaucophane Jadeite Pumpellyite | Garnet | Monoclinic / Triclinic |
| Chromite | Reddish / Deep Brown / almost Opaque | Isotropic if translucent | Very High | Simple Twinning | None | Isotropic | Cubes / Octahedral / Small grains | Isotropic | Isotropic | Igneous (Mafic and Ultramafic) | Clinopyroxenes Melanite Nepheline Olivine Sodalites Volcanic Glass / Never With Quartz | Oxide / Spinel | Cubic |
| Chrysotile / White Asbestos | Colourless to Pale Green / Weakly Pleochroic | Very Low | Low to Very High | Asbestos forming in fractures | Straight | Fibrous / Radiating | Small to Large 10-90° (if Positive) / 30-35° (if Negative) | Positive / Negative | Metamorphic (Hydrothermally altered ultrabasic and basic rocks and Greenschist Facies) | Bornite Chalcopyrite Galena Ilmenite Pentlandite Pyrite Pyrrhotite Sphalerite | Serpentine | Monoclinic | |
| Clinozoisite | Colourless | Low to Moderate. 0.004-0.015 Anomalous | Moderate | Anomalous steel-blue birefringence | Good | Straight parallel to side / Inclined to cleavage | Prisms | Moderate to Large 40-90° | Positive | Metamorphic (Low to High grade regional metamorphism, Contact Metamorphism, Blueschist) | Biotite Hornblende MuscoviteK-Feldspar Plagioclase Quartz | Epidote | Monoclinic |
| Cordierite | Colourless | Low. 0.008 up to White | Low | Often Spongy, Porous / may alter to yellow Pinite along cracks and margins / Twinning / Yellow pleochroic haloes around radioactive inclusions / Inclusions of Biotite and Quartz or Graphite in metamorphic rocks | Poor | Straight | Irregular / Hexagonal / Spongy | Moderate to Large 35-80° | Negative | Metamorphic (Low-P metapelites) / rare in igneous | Albite Almandine Biotite Quartz Chlorite Kyanite MicroclineK-Feldspar Plagioclase Quartz Staurolite | Ring Silicate | Orthorhombic |
| Corundum | Colourless to Reddish or Blue / Pleochroic | Low (up to 1st order Yellow) | High | May have zoned colour distribution with pleochroism / Lamellar Twinning / Length Fast | Good. 2 sets at 94° | Straight | Plates / Hexagonal / Needles / Prisms | Uniaxial | Negative | Metamorphic (Al-rich and silica-poor contact metamorphism, regional Schists) | Aegirine-Augite Apatite Leucite Melanite Melilite Olivine Sodalites Titanaugite / Never With Quartz | Trigonal | |
| Cristobalite | Colourless | Very Low to Low | Very Low | Lamellar Twinning / Occurs in cavities in Si-oversaturated igneous rocks / Devitrification product in high T metamorphic rocks (Sanidine facies) | Straight | Plates / Spherulitic / Needles / Chalcedony-Like /Tabular Prisms / Fibrous | Uniaxial or Biaxial Small 2V (25°) | Uniaxial Positive / Biaxial Negative | Igneous (Fractures of acidic to intermediate Volcanic rocks) / Metamorphic (Sanidinite facies Contact metamorphism) | Clinopyroxenes Leucite Melanite Nepheline Olivine Plagioclase Volcanic Glass Sanidine Titanaugite | Framework SiO2 | Pseudo Cubic | |
| Crossite | Pale Yellow / Purple / Blue / Pleochroic | Moderate. 0.02 | Moderate | May be zoned | Good. 2 sets at 124° | Inclined 5-10° | Prisms / Fibrous | Small to Moderate 0-50° | Negative | Metamorphic (Glaucophane Schist, Eclogite) | Chromite Clino And Orthopyroxenes Plagioclase Serpentine | Alkali Amphibole | Monoclinic |
| Cummingtonite | Colourless to Pale Brown | Moderate to High. 0.02-0.045 | Moderate to High | Lamellar Twinning | Good. 2 sets at 124° (Amphibole Cleavage) | Inclined 10-20° | Prisms | Moderate to Large 60-85° | Positive or Negative | Metamorphic / rare in igneous | Rutile Garnet Kyanite Zoisite | Amphibole | Monoclinic |
| Diopside | Colourless / Pale Brownish / Greenish | Moderate to High. up to upper 2nd order | High | Rare Simple Twinning / Exsolution Lamellae in Orthopyroxene / Alters to Amphibole and Serpentine | Good. 2 sets at 90° | Inclined 35-50° | Prisms | Moderate 50-70° | Positive | Igenous (Basic rocks, Kimberlites) / Metamorphic (Marbles, High grade metabasite) | Biotite Hornblende Microcline Plagioclase Quartz Sericite Sphene | Clinopyroxene | Monoclinic |
| Dolomite | Colourless / Brown tinged | Very High. 0.179 | Low to High | Lamellar Twinning / Commonly iron-oxide dusted / Coarser Lamellae than Calcite / Length Fast | Perfect | Inclined to Cleavage | Prisms | Uniaxial | Negative | Metamorphic / Sedimentary | Carbonate | Trigonal | |
| Enstatite | Colourless / Weakly Pleochroic | Very Low | Moderate to High | Zoning with Mg-rich core in Colcanic rocks / often with exsolution lamellae in Plutonic rocks / Alters to serpentine | Good. 2 sets | Straight | Short Columns / Elongate Prisms / Granular | Moderate to Large 54-83° | Positive | Igneous (Basic to ultrabasic rocks) | Orthopyroxene | Orthorhombic | |
| Epidote | Colourless, Yellow or Greenish / Pleochroic Yellow Orange to Red Purple | Moderate to High. 0.015-0.05 up to 3rd order / May be Anomalous | High | Occurs as accessory mineral in granitic rocks | Good | Straight or Inclined | Prisms / Granular / Hexagonal / Radiating | Moderate Large 60-90° | Positive or Negative | Metamorphic (Low-Grade metabasalts, Blueschist, Contact Metamorphism) | Leucite Magnetite Melilite Nepheline Sodalites / Never Ilmenite | Epidote | Monoclinic |
| Epistilbite | Colourless | Very Low | Very Low | High birefringence compared to other zeolites / Simple Twinning / Length Slow | Inclined 10° | Radial / Fibrous Aggregates / Laths | Moderate to Small 44° | Positive | Metamorphic (Hydrothermal Amygdules in Basalts and Andesites) | Albite Almandine Biotite Quartz Chlorite Kyanite MicroclineK-Feldspar Plagioclase Quartz Staurolite | Flaky Zeolite | Monoclinic | |
| Fluorite | Colourless / Blueish / Purple | Isotropic | Very High Negative | Often purple due to radiation damage / Occurs as cement in sandstones / Zonal growth rings / Mottled colour texture / Found in Hydrothermal veins | Perfect. 3 sets at 60°/ 2 Sets at 70 | Isotropic | Cubes / Octahedral / Typically Massive | Isotropic | Isotropic | Igenous / Sedimentary | Calcite Diopside Leucite Melilite Nepheline Olivine Pyrope | Fluorite | Cubic |
| Garnet Group | Colourless to Pale Pink (most common) | Isotropic | High | May be zoned / May have trails with Quartz and Biotite inclusions, which may have S or Z shapes / May alter to chlorite | None | Isotropic | Hexagonal / Octogonal | Isotropic | Isotropic | Metamorphic / rare in igneous | Garnet | Cubic | |
| Gedrite | Colourless | Low to Moderate. 0.013 | Moderate | Good. 2 sets at 124° (Amphibole Cleavage) | Straight | Prisms | Large | Positive | Metamorphic | Clinopyroxenes Leucite Nepheline Olivine Plagioclase Sodalites | Amphibole | Orthorhombic | |
| Gehlenite | Colourless / Yellow / Weakly Pleochroic | Low / May be anomalous Purple Blue | Moderate | Interpenetrating twinning / Length Slow | Poor. 2 sets | Straight | Short Prisms / Granular | Uniaxial | Negative | Igneous (Silica-undersaturated Volcanic rocks) / Metamorphic | Biotite Clinopyroxene Olivine Hornblende MicroclineK-Feldspar Orthopyroxene Quartz Titanaugite Volcanic Glass | Melilite | Tetragonal |
| Glauconite | Green / Pleochroic | Very High | Moderate | Never as oolite (as opposed to chamosite) / Length Slow | Pefect | Inclined 2-3° | Spheres / Elliptic | Small 0-20° | Negative | Metmorphic (Marbles) / Sedimentary (Sandstones) | Monoclinic | ||
| Glaucophane | Pale Yellow / Purple / Blue / Pleochroic | Moderate. 0.02 up to Low 2nd order | Moderate | May be zoned / Length Slow | Good. 2 sets at 124° | Inclined 5° | Prisms / Fibrous | Small to Moderate 0-50° | Negative | Metamorphic (High P Low T) | Albite Biotite Hornblende K-Feldspar Microcline Plagioclase Sphene Volcanic Glass | Alkali Amphibole | Monoclinic |
| Goethite | Yellow / Orange Brown / Pleochroic | Very High | Very High | Component of Limonite | Good | Straight | Needles / Radial Fibrous / Oolitic spheres | Small | Negative | Igneous / Metamorphic (in weathered and altered Fe-minerals and rocks, Cavity and Fracture Filling, Fe-ore deposits) | Aegirine-Augite K-Feldspar Anorthoclase Nepheline Riebeckite Sodalite | Oxide | Orthorhombic |
| Graphite | Greenish Gray / Opaque | Very Low to Very High | Smeared margins / Often in Barrovian foliated rocks (e.g. Phyllite or Gneisses) | Perfect | Flakes / Grains | Metamorphic | Biotite Cordierite Corundum Kyanite Quartz Spinel | Hexagonal | |||||
| Grossularite | Colourless / Green to Yellow | Isotropic (may be anomalous) | High | Zonal growth rings / Mottled colour texture | None | Isotropic | Euhedral (Rhombic Dodecahedrons; like a Hexagon with more faces) / Anhedral Grains | Isotropic | Isotropic | Metamorphic (e.g. Marbles) / Sedimentary (e.g. Limestones) | Biotite Clinopyroxenes Hornblende Orthopyroxenes Plagioclase Quartz | Garnet | Cubic |
| Grünerite | Colourless to Pale Brown | Moderate to High. 0.02-0.045 | Moderate to High | Lamellar Twinning | Good. 2 sets at 124° (Amphibole Cleavage) | Inclined 10-20° | Prisms | Moderate to Large 60-85° | Positive or Negative | Metamorphic / rare in igneous | Amphibole | Monoclinic | |
| Gypsum | Colourless | Very Low | Very Low to Low | Tends to be distorted / Polysynthetic twinning can form during thin-section making / Simple Twinning | Good. 3 sets | Inclined 15° | Plates / Fibrous / Granular | Moderate to Small 58° | Positive | Sedimentary | Monoclinic | ||
| Harmotome | Colourless | Very Low | Very Low | Heating during thin-section making changes the optical characteristics | Inclined 28-32° | Thick Columns / Elongate Prisms | Large to Small 79° | Positive | Igneous (Cavity and Fractures Filling in basic Volcanic rocks, in veins in plutonic rocks) | Cubic Zeolite | Monoclinic | ||
| Hastingsite Group | Bright Green to Yellow Green / Pleochroic | Very Low | Moderate to High | May have pleochroic haloes / Use associated minerals to distinguish from other amphiboles / Alters to Actinolite, Antigorite, Chlorite / Length Slow | Inclined 14-20° | Short to Long Columns / Needles / Elongate Prisms | Moderate to Large 34-90° | Negative | Igneous (Intermediate to acidic rocks and Lamprophyrs) / Metamorphic (Amphibolite and Amphibole Schists) | Andalusite Biotite Cordierite K-Feldspar Kyanite Muscovite Plagioclase Quartz | Green Hornblende Amphibole | Monoclinic | |
| Haüyne | Colourless / Blue / Purple Blue / Blue Green | Isotropic | Moderate Negative | Dark rims, opaque streaks and clusters / Zoned / Irregular colour distribution / Locally as fine-grained inclusions | Good | Isotropic | Hexagonal / Cubes / Anhedral / Corroded crystals / | Isotropic | Isotropic | Igneous (Mainly alkaline volcanic, rarely plutonic) | Leucite Nepheline | Sodalite (Feldspathoid) | Cubic |
| Hematite | Blood Red / Opaque | Not detectable | Very High | Normally Opaque / Grains may be deep Red on thin edges / Mainly in schists or as accessory mineral in other rocks. | None | Straight | Hexagonal Plates / Granular / Tabular / Fibrous | Uniaxial (Opaque) | Negative | Igneous / Metamorphic (Low to Medium grade) / Sedimentary | Clinopyroxenes Leucite Melanite Nepheline Olivine Titanaugite Volcanic Glass / Never With Quartz | Oxide | Trigonal |
| Hercynite | Deep, "Emerald" Green | Isotropic | High | May be zoned with a darker core / Simple Twinning | Isotropic | Octahedral / Granular | Isotropic | Isotropic | Igneous (Ultramafic rocks) / Metamorphic (Cordierite Sillimanite Gneisses) | Aegirine-Augite Apatite Nepheline K-Feldspar Plagioclase Quartz Sanidine | Spinel | Cubic | |
| Heulandite | Colourless | Very Low | Very Low | Simple Twinning / May occur as Devitrification Product / Length Fast | Perfect | Inclined 0-32° | Platy / Flaky / Radiating / Rosettes / Subparallel Aggregates | Small to Moderate 0-50° | Positive | Igneous (Cavity and Fractures Filling in acidic to basic magmatic rocks) / Metamorphic (in metatuffs and metagreywackes in Zeolite facies) | Almandine Cordierite Corundum | Flaky Zeolite | Monoclinic |
| Hornblende | Green / Brown / Red / orange / Pleochroic | Low to Moderate. 0.015-0.02 up to mid 2nd order | High | Colour of metamorphic Hornblendes often related to grade: Low to high grade goes from Bluish Green to Green to Brownish / Occurs in intermediate Igneous rocks / Occurs in medium grade metamorphic rocks | Good. 2 sets at 120° | Inclined 2-4° | Elongate Prisms / Laths | Moderate to Large 50-80° | Negative | Igneous / Metamorphic (Med grade) | Albite Almandine Biotite Kyanite Muscovite Quartz | Amphibole | Monoclinic |
| Hypersthene | Pale Green / Reddish / Pale Brown / Weakly Pleochroic | Very High | Moderate to High | Outdated term for a mineral in the Enstatite-Ferrosilite series / Zoning with Mg-rich core in Colcanic rocks / often with exsolution lamellae in Plutonic rocks / Alters to serpentine | Good. 2 sets | Short Columns / Granular / Elongate Prisms | Moderate 63-45° | Negative | Igneous (Intermediate to acidic Volcanic rocks) / Metamorphic (Contact metamorphism, Pyroxene Granulites) | Calcite Glaucophane Chlorite Garnet Quartz Sericite Sphene | Orthopyroxene | Orthorhombic | |
| Illite | Colourless | High. 0.030-0.035 | Low | Coats grain surface / Extremely fine | Perfect | - | Fibrous / Wispy / Very fine | Small 5-25° | Negative | Sedimentary | Antigorite Actinolite Clinochore Quartz Tremolite | Mica | Monoclinic |
| Ilmenite | Red in thin flakes or Opaque | Not detectable | Very High | Common accessory mineral | None | Straight | Hexagonal Plates / Laminar / Prismatic / Skeletal / Granular / Flaky | Uniaxial (Opaque) | Negative | Igneous / Metamorphic (High grade) / Sedimentary | Apatite Beryl Cassiterite Fluorite Spodumene Topaz | Oxide | Trigonal |
| Jadeite | Colourless to Pale Green / Weakly Pleochroic | Low. 0.006 anomalous | Moderate | Occurs in Glaucophane rocks and Jadeite-Quartzites | Good. 2 sets at 87° | Inclined 30-50° / May be Undulose | Prisms / Hexagonal / Needles | Large 60-90° | Positive | Metamorphic | Albite Epidote Biotite Sphene Talc Calcite Chlorite Quartz Sericite | Clinopyroxene | Monoclinic |
| Kaersutite | Reddish Brown / Pleochroic | Very High | Moderate to High | May have zoned colour distribution / Hourglass structure / Reaction Rims / Length Slow | Inclined 3-19° | Short Columns / Elongate Prisms | Large 74-82° | Negative | Igneous (Na-rich basic rocks) | Cristobalite | Brown Hornblende Amphibole | Monoclinic | |
| Kaolinite | Colourless / Pale Yellow | Low. 0.007 | Low | Stacks of tiny plates / Often fills pore space / from the alteration of Feldspars | Perfect | - | Plates / Fibrous / Radiating platelets | Small to Moderate 25-50° | Negative | Sedimentary | Calcite Diopside Epidote Grossularite Quartz Vesuvianite | Clay / Sheet | Triclinic / Monoclinic |
| Katophorite | Greenish Brown | Very Low | Moderate to High | May have zoned colour distribution / Hourglass structure / Reaction Rims / Length Slow | Inclined 8-16° | Small to Moderate 0-57° | Negative | Igneous (Na-rich Magmatites) | Brown Hornblende Amphibole | Monoclinic | |||
| Koppite | Colourless / Red to Brown | Isotropic | Very High | Simple Twinning / Hard to differentiate from Perovskite, Picotite, Cromite and Melanite | Isotropic | Euhedral (Dodecahedrons; like a Hexagon with more faces) | Isotropic | Isotropic | Igneous (Carbonatites) | Apatite Biotite Hornblende Or Nepheline K-Feldspar Quartz | Cubic | ||
| Kyanite | Colourless / Pale Blue Pleochroic | Low. 0.012-0.016 up to 1st order Yellow | High > Andalusite and Sillimanite | Stress induced curving / Length Slow | Perfect. 2 sets at 85° | Inclined 0-30°max | Prisms | Large 85° | Negative | Metamorphic (Moderate to high grade metapelites) | Actinolite Albite Chlorite Clinozoisite Epidote Prehnite Sericite | Al Silicate | Triclinic |
| Labradorite | Colourless | Low. up to White | Low | Albite Twinning lengthways / Carlsbad Twinning / Often zoned: typically Anorthite (Na-rich) centres and Albite (Ca-rich) rims. Anorthite cores tend to alter to a fine-grained, turbid, white mica (Sericite) / Often with Clinopyroxene and/or Olivine in Igenous rocks. | Perfect and Good. 2 sets at 86° | Inclined 28-39° | Prisms / Rectangular Laths | Large 70-90° | Negative | Igenous / Metamorphic (High grade) | Fluorite K-Feldspar Li-Mica Quartz Rutile Topaz Tourmaline | Plagioclase Feldspar | Triclinic |
| Laumontite | Colourless | Very Low | Very Low | Extinction angle related to degree of water loss / Length Slow | Inclined 8-11° | Radial / Columns / Elongate Prisms / Spherulitic | Moderate 33-47° | Negative | Igneous (Cavity and Fractures Filling in acidic to basic magmatic rocks) / Metamorphic (in metatuffs and metagreywackes in Zeolite facies) | Zircon Cassiterite Ilmenite Rutile | Mordenite Fibrous Zeolite | Monoclinic | |
| Lawsonite | Colourless / Rare Blueish | Moderate. 0.020 | Moderate | Lamellar Twinning / Length Fast / in Glaucophane schists, Greenschist and amphibolites | Perfect. 2 sets | Straight / May be Undulose | Diamond / Prisms / Plates | Large 76-87° | Positive | Metamorphic | Leucite Nepheline Olivine Perovskite Pyroxene Never With Quartz | Epidote | Orthorhombic |
| Lepidolite | Colourless / Pale pink / Weakly Pleochroic | Very High | Very Low to Moderate | Pleochroic haloes around zircon / Occurs as fine-speckled in extinction orientation / Length Slow | Perfect | Straight (Parallel to Cleavage) | Platy / Flaky / Scaly / Columns | Small to Moderate 23-58° | Negative | Igneous (Li-rich Granite Pegmatites) / Metamorphic (Greisen) | Leucite Nepheline Olivine Perovskite Pyroxene Never With Quartz | Lithionite Series Mica | Monoclinic |
| Leucite | Colourless | Very Low. Almost Isotropic. 0.001 / Anomalous | Moderate Negative | Multiple Twinning / Volcanic only | Poor | Straight | Euhedral (Icositetrahedral) / Trapeze shaped | Almost Isotropic | Positive | Igneous | Opal Zeolites | Feldspathoid | Tetragonal / Pseudo Cubic |
| Limonite | Ochre-Yellow to Reddish-Brown | Very Low / Opaque if dendritic | Very High to Very Low | Broad term for unidentifiable massive Fe oxides / No visible crystals / Most commonly just Goethite | None | Oolitic spheres / Crust and Soil-Like / Radiating | From alteration of Hematite or Magnetite / Igneous / Metamorphic / Sedimentary | Cristobalite Tridymite Volcanic Glass | Oxide | - | |||
| Lizardite | Colourless to Pale Green / Weakly Pleochroic | Very Low | Low | Main phase in Bastite (Pseudomorphous after orthopyroxenes) / Length Slow | Perfect | Straight | Fine-Scaly / Fibrous | Small 0° | Negative | Metamorphic (Serpentinites) | Analcite Calcite Zeolites | Serpentine | Monoclinic |
| Magnesite | Colourless / Gray Brown | Very High | Very Low to High | May have Lamellar Twinning / Length Fast | Straight | Granular / Fibrous / Dense | Uniaxial | Negative | Metamorphic (Talc and chlorite schist, as gel in serpentinites, as ore deposit in metasomatic zones) | Carbonate | Trigonal | ||
| Magnetite | Opaque | Isotropic if translucent | Very High | Magnetic / AKA Lodestone | None | Isotropic | Cubes / Octahedral / Granular / Skeletal | Isotropic | Isotropic | Igneous / Metamorphic / Sedimentary | Oxide | Cubic | |
| Melanite | Brown | Isotropic | Very High | Zonal texture | None | Isotropic | Euhedral (Rhombic Dodecahedrons; like a Hexagon with more faces) / Anhedral Grains | Isotropic | Isotropic | Igneous (Alkaline rocks) | Garnet | Cubic | |
| Mesolite | Colourless | Very Low | Very Low | Isotypic (Similar crystal structure and chemical formula) with Natrolite and Scolecite / Length Fast | Inclined 2-5° | Fibrous | Large to Small 80° | Positive | Igneous (Cavity filling in phonolites and basalts) | Natrolite Fibrous Zeolite | Monoclinic | ||
| Microcline | Colourless | Low. 0.006-0.010 up to Gray | Very Low | Cross-hatch Twinning | Perfect. 2 sets | Inclined | Prisms | Moderate to Large 60-80° | Negative | Igneous / Metamorphic (Med to High Grade) / Sedimentary | Calcite Epidote Fassaite Grossularite Sphene Spinel Wollastonite | Alkali Feldspar | Triclinic |
| Monazite | Colourless / Green - Yellow / Weakly pleochroic | High to Very High | High | Simple Twinning / May be fractured / May look like Zircon or Sphene / Higher birefringence and less pleochroic than Staurolite | Good | Straight / May be Inclined 2-6° | Tabular / Plates | Small 10-25° | Positive | Igneous (Granites) / Metamorphic (Dolostones and Mica Schists) / Sedimentary (highly resistant to weathering) | Epidote Cordierite Apatite Ilmenite Bastnasite | Phosphate | Monoclinic |
| Mordenite | Colourless / Red | Very Low | Very Low | May occur as Devitrification Product | Good | Straight | Fibrous / Radial / Fine grained | Large 76-90° | Positive / Negative | Igneous (Cavity and Fractures Filling in acidic Volcanic rocks) / Sedimentary | Cassiterite Li-Mica Quartz Topaz Tourmaline | Mordenite Fibrous Zeolite | Orthorhombic |
| Muscovite | Colourless / Pale Yellow / Pale Green (Cr-rich) | High. 0.036-0.04 up to upper 2nd order | Moderate | Cleavage kink due to deformation / Length Slow | Perfect | Straight or 1-2° (Undulose) | Plates / Fine aggregates / Flakes | Moderate 30-50° | Negative | Igneous (Al-rich granites) / Metamorphic / Sedimentary | Calcite Zeolite | Mica | Monoclinic |
| Natrolite | Colourless | Very Low | Very Low | Pseudomorphous after Plagioclases / Length Slow | Good | Straight | Radiating Needles / Lath / Fibrous / Radiating Aggregates | Moderate 58-64° | Positive | Igneous (Cavity filling in basic to intermediate magmatic rocks) | Clinopyroxenes Olivine Plagioclase Spinel | Natrolite Fibrous Zeolite | Orthorhombic |
| Nepheline | Colourless / Cloudy from inclusions | Low. 0.009-0.005 (<quartz) up to dark Gray | Low Negative | Euhedral blocky shapes (i.e. hexagons or rectangles) are only seen in lavas, Anhedral elsewhere / Length Fast | Poor | Straight | Hexagonal / Prisms / Euhedral blocks | Uniaxial | Negative | Igneous (Alkali rocks) | Clinopyroxenes Olivine Plagioclase Spinel | Feldspathoid | Hexagonal |
| Nosean | Colourless | Isotropic | Moderate Negative | Dark rims, opaque streaks and clusters / Zoned / Irregular colour distribution / Locally as fine-grained inclusions | Poor | Isotropic | Hexagonal / Cubes / Anhedral corroded crystals / | Isotropic | Isotropic | Igneous (Mainly alkaline volcanic, rarely plutonic) | Biotite Clinopyroxenes Hornblende Plagioclase Volcanic Glass | Sodalite (Feldspathoid) | Cubic |
| Oligoclase | Colourless | Low. up to White | Very Low | Albite Twinning lengthways / Carlsbad Twinning / Often zoned: typically Anorthite (Na-rich) centres and Albite (Ca-rich) rims. Anorthite cores tend to alter to a fine-grained, turbid, white mica (Sericite) / Often with Biotite and K-feldspar in Igneous rocks / In low-med grade metamorphic rocks | Perfect and Good. 2 sets at 86° | Inclined 12° | Prisms / Rectangular Laths | Large 70-90° | Negative | Igenous / Metamorphic (Low grade) | Clinopyroxenes Leucite Nepheline Olivine Plagioclase Sodalites | Plagioclase Feldspar | Triclinic |
| Olivine Group | Colourless (Mg-rich) to Yellow or Pale Brown (Fe-rich) | High. 0.032-0.05 up to upper 2nd order, or 3st in Fayalite (Fe-rich Olivines) | High | May have different birefringence colours along curving cracks / May alter to serpentine / Occurs in basic and ultrabasic igneous rocks / Occurs in meta marbles / Fayalite (Fe-rich olivines) rare in granitic and syenitic rocks. | None. Curving Cracks | Straight | Diamond / Hexagonal / Octahedral / Granular | Uniaxial | Positive for Forsterite (Mg-rich) / Negative for Fayalite (Fe-rich) | Igneous (Basic to Ultrabasic) / Metamorphic (e.g. Serpentinites, Marbles) | Biotite Garnet MicroclineK-Feldspar Plagioclase Pyroxene Quartz Sphene | Olivine | Orthorhombic |
| Omphacite | Colourless to Pale Green / faintly Pleochroic | Low. 0.012 moderately anomalous | Moderate to High | Like Augite but with lower Birefringence | Good . 2 sets at 87° | Inclined 34-48° | Prisms / Hexagonal | Moderate to Large 55-85° | Positive | Metamorphic (Only Eclogites) | Biotite Garnet MicroclineK-Feldspar Plagioclase Pyroxene Quartz Sphene | Clinopyroxene | Monoclinic |
| Opal | Colourless / Yellowish / Reddish | Anomalous | Very Low | Often altered to Cristobalite or Chalcedony / Shrinkage cracks / Hydrated SiO2 | Not a crystal | Amorphous / Spherical | Not a crystal | Not a crystal | Igneous (Volcanic) | Albite Almandine Epidote | Oxide | ||
| Orthoclase / K-Feldspar | Colourless | Low. 0.006-0.010 up to Gray | Low | Carlsbad Twinning / Perthitic Exsolution common / Often turbid | Perfect. 2sets at 90° | Straight | Prisms | Large 60-80° | Negative | Igneous (Acid to Intermediate rocks, Volcanic) / Metamorphic (Orthogneiss) | Biotite Clinopyroxene Orthopyroxene Plagioclase Volcanic Glass | Alkali Feldspar | Monoclinic |
| Orthopyroxene Group | Colourless to Pale Pink / Green Pleochroic | Low. 0.007 to Moderate at Ferrosilite (Fe-rich). up to 1st order Yellow | Moderate to High | Pleochroic grains usually have a negative optic sign / Occurs in basic and ultrabasic rocks / Occurs in high-grade metamorphic rocks (i.e. metabasites) / Length Fast | Good. 2 sets at 87° | Straight | Prisms / Hexagonal | Moderate to Large 55-90° | Positive for 88-100 Fe% / Negative at 12-88 Fe% | Igneous / Metamorphic | Olivine Plagioclase Titanaugite | Pyroxene | Orthorhombic |
| Oxybiotite | Red to Dark Brown | Very Low | Moderate to High | Reaction Rims / Pleochroic haloes around Zircon / Occurs as fine-speckled in extinction orientation / Length Slow | Perfect | Straight (Parallel to Cleavage) | Platy / Flaky / Scaly / Columns | Small 20-30° | Negative | Igneous (Intermediate Volcanic rocks) | Aegirine-Augite Apatite Arfvedsonite Nepheline Sanidine Olivine Titanbiotite | Mica | Monoclinic |
| Oxyhornblende | Red to Dark Brown | Very Low | Moderate to High | Changeable relief and birefringence in a single crystal / Haloes / Reaction Rims / Length Slow | Perfect. 2 sets at 124° | Straight to Inclined 12° | Short to Long Columns | Moderate to Large 56-88° | Negative | Igneous (Acidic to intermediate Volcanic rocks) | Aegirine-Augite Anorthoclase K-Feldspar Nepheline Riebeckite Sodalite | Brown Hornblende Amphibole | Monoclinic |
| Paragonite | Colourless | High. 0.036-0.04 | Moderate | Perfect | Straight or 1-2° (Undulose) | Plates | Moderate 40° | Negative | Metamorphic / Sedimentary | Beryl Cassiterite Quartz Spodumene Topaz Tourmaline | Mica | Monoclinic | |
| Perovskite | Colourless / Dark Brown / Yellowish / Greenish | Isotropic / Very weak / Anomalous | Very High | May have zoned colour distribution / Very small grains are opaque / Simple and Lamellar Twinning | Poor | Almost Isotropic | Octahedral / Cubes | Almost Isotropic | Positive | Igneous (Kimberlites, Alkaline and Volcanic rocks) | Cassiterite Quartz Topaz Wolframite | Pervoskite | Orthorhombic |
| Phengite | Colourless / Pale Green | High. 0.036-0.04 | Moderate | A Si-rich Muscovite / Can't be distinguished from Muscovite Optically / Length Slow | Perfect | Straight or 1-2° (Undulose) | Fine aggregates / Flakes | Moderate 25-35° | Negative | Igneous / Metamorphic (Glaucophane schist, Eclogite, Gneiss) | Clino And Orthopyroxenes Oxyhornblende Plagioclase Quartz Volcanic Glass Sanidine | Mica | Monoclinic |
| Phillipsite | Colourless | Very Low | Very Low | Interpenetrating Twinning / Occurs in basalt cavities / Length Slow | Inclined 11-30° | Thick Columns | Moderate to Large 60-80° | Positive | Igneous (Cavity and Fractures Filling in basic Volcanic rocks, Nepheline syenite) | Aegirine-Augite Apatite Na-Sanidine Nepheline Nosean | Cubic Zeolite | Monoclinic | |
| Phlogopite | Colourless / Pale Yellow and Green / Orange / Pink / Brown | High. 0.028-0.045 | Low to Moderate | A Mg-rich Mica / Pleochroic Haloes around inclusions / Length Slow | Perfect | Straight or slightly Inclined | Needles / Elongate Laths / Micaceous Flakes | Small <15° | Negative | Igneous (Basic and Ultrabasic, Kimberlites) / Metamorphic (Marbles) | Calcite Pyrite Quartz | Biotite Mica | Monoclinic |
| Picotite | Yellow to Brown | Isotropic | Very High to Very Low | Occurs as small inclusions in Olivines or Serpentine / Simple Twinning | Isotropic | Granular within Olivine or Serpentine | Isotropic | Isotropic | Igneous (Alkali basalts) | Calcite Chlorite Chrysotile Olivine Pyroxene Zeolite | Spinel | Cubic | |
| Piemontite | Yellow / Pink / Magenta / Deep Brown Pleochroism | Low to High. 0.025-0.075 / May be Anomalous | High | A Mn-rich Epidote | Good. 2 sets | Straight or Inclined | Prisms | Moderate to Large 50-85° | Positive | Metamorphic | Hornblende Microcline OlivineK-Feldspar Pyroxene Quartz Serpentine | Epidote | Monoclinic |
| Pigeonite | Colourless to Greenish Pinkish or Brownish | Moderate to High. 0.023-0.029 | Moderate to High | May alter along cracks / Lamellar Twinning / Often as matrix | Good. 2 sets at 87° | Inclined 37-44° | Prisms / Hexagonal | Small 0-30° | Positive | Igneous (Ti-rich Alkali Rocks) | Amphibole Biotite Delessite Pyroxene | Clinopyroxene | Monoclinic |
| Plagioclase Group | Colourless | Very Low. 0.007-0.013 | Low | Lamellar Twinning | Perfect | Inclined | Prisms | Large | Positive for Ab 77, Negative for An 78 | Igneous / Metamorphic / Sedimentary | Actinolite Albite Biotite Epidote Glaucophane Lawsonite Pumpellyite Quartz Sericite Zoisite | Plagioclase Feldspar | Triclinic |
| Pleonaste | Greenish Gray | Isotropic | High to Very Low | Simple Twinning | Isotropic | Octahedral | Isotropic | Isotropic | Igneous (Mafic) / Metamorphic (e.g. Marbles) | Chrysotile Magnesite Olivine Orthopyroxene Talc | Spinel | Cubic | |
| Prehnite | Colourless | Very Low / May be Anomalous Blue to Brown | Moderate | Lamellar Twinning | Good | Straight | Plates / Flaky / Radiating Aggregates / Dendritic / Skeletal | Moderate to Large 64-71° | Positive | Igneous (Basic Volcanic rocks) / Metamorphic (Greenschists, metabasalts and in metamorphic siliceous limestones) | Alumino-Silicate | Orthorhombic | |
| Pumpellyite | Colourless / Green / Blue-Gray / Brownish / Pleochroic | Low to Moderate / May be anomalous Blue to Brown | Moderate to High | Twinning / Zoned / Intergrown with Lawsonite | Good. 2 sets | Inclined 5-22° | Radiating Rays / Laths / Needles / Fibrous / Rosettes | Small to Large 7-110° | Positive or Negative | Metamorphic (Green and Blueschist) | Antigorite Bronzite Chrysotile | Pumpellyite Epidote | Monoclinic |
| Pyrite | Opaque | Isotropic | High | Hard to ID in Transmitted light / Often weathered / Interpenetrating Twinning | Isotropic | Octahedral / Cubes / Granular | Isotropic | Isotropic | Igneous / Metamorphic (Schists) / Sedimentary | Aegirine-Augite Aenigmatite Arfvedsonite Quartz Volcanic Glass | Cubic | ||
| Pyrochlore | Reddish to Opaque Brown | Isotropic | Very High | Simple Twinning / Hard to differentiate from Perovskite, Picotite, Chromite and Melanite | Isotropic | Octahedral / Granular | Isotropic | Isotropic | Igneous (Pegmatites and Volcanic ejections) | Analcite Calcite Heulandite Laumontite Na-Sanidine Nepheline Scolecite Stilbite Thomsonite | Cubic | ||
| Pyrope | Pale Red | Isotropic | Very Low | Celyphytic rims common | None | Isotropic | Euhedral (Rhombic Dodecahedrons; like a Hexagon with more faces) / Anhedral Grains | Isotropic | Isotropic | Metamorphic (Peridotites, Kimberlites, Serpentinites and Eclogites) | Calcite Chalcedony Zeolite | Garnet | Cubic |
| Pyrrhotite | Opaque | Very Low | Hard to ID in Transmitted light | Granular / Tabular/ Massive | Igneous (Mafic to Ultramafic) | Albite Analcite Calcite Chabazite Chalcedony Chlorite Heulandite Natrolite Scolecite Stilbite Thomsonite | Hexagonal | ||||||
| Quartz | Colourless | Low. 0.009 up to cream | Low | Length Slow | None | Straight if Prisms edge visible (may be Undulose) | Irregular Prisms | Uniaxial | Positive | Igneous / Metamorphic (Low grade) / Sedimentary | Albite Analcite Calcite Chabazite Chalcedony Chlorite Heulandite Natrolite Scolecite Stilbite Thomsonite | Framework SiO2 | Trigonal |
| Riebeckite | Green / Purple / Brown / Dark Blue / Pleochroic | Low. 0.006-0.016 / May be anomalous | Moderate to High | Length Fast | Good. 2 sets at 124° | Inclined 3-15° | Short Prisms / Needles | Moderate to Large 40-100° | Negative to Positive | Igneous (Na-rch) / Metamorphic | Heulandite Laumontite Stilbite | Alkali Amphibole | Monoclinic |
| Rutile | Deep Reddish Brown / Yellow Brown / Opaque | Very High. 0.29 | Very High | Occurs in coarse-grained, high pressure, metamorphic rocks (e.g. eclogites, or kyanite-bearing) / Occurs in Igneous rocks as tiny grains (may be opaque) / May have radioactive haloes / Length Slow | Good | Straight (Not easy to see) | Granules / Plates | Uniaxial | Positive | Metamorphic (High-P) / Igneous | Albite Apophyllite Calcite Chlorite Epidote Prehnite Quartz Zeolite | Oxide | Tetragonal |
| Sanidine | Colourless | Low. 0.006-0.008 | Low | Small 2V is key / Carlsbad Twinning | Perfect | Straight | Prisms | Small to Moderate 0-60° | Negative | Igneous | Analcite Laumontite Quartz Stilbite | Alkali Feldspar | Monoclinic |
| Sapphirine | Colourless / Pale Blue Pleochroic | Very Low to Low. 0.005-0.009 anomalous | High | Often in Symplectite associations | Moderate | Straight or slightly Inclined | Irregular | Moderate to Large | Negative | Metamorphic | Calcite Clay Minerals Heulandite Laumontite Quartz | Pyroxene | Monoclinic |
| Scapolite Group | Colourless / Yellow | Very Low (Na) to High (Ca) | Low to Moderate | May be cloudy / Fluid and mineral inclusions common / Scapolite group is a series between Marialite and Meionite | Good. 2 sets | Straight or symmetrical to cleavage | Cubes / Prisms | Uniaxial | Negative | Igneous / Metamorphic | Chabazite Heulandite Laumontite Mordenite Scolecite Stilbite | Framework | Tetragonal |
| Scolecite | Colourless | Very Low | Very Low | Simple Twinning / Length Fast | Good | Inclined 15-18° | Fibrous / Radial | Moderate 36-58° | Negative | Igneous (Amygdules in basic to ultramafic magmatic rocks) / Metamorphic (Fracture filling) | Analcite Calcite Chabazite Chalcedony Natrolite Thomsonite | Natrolite Fibrous Zeolite | Monoclinic |
| Sericite | Colourless | Moderate to High | Low to Moderate | From the hydrothermal alteration of Orthoclase or Plagioclase / Variety of Muscovite | Good | Straight | Flakes / Irregular Granules | Moderate 30-50° | Negative | Metamorphic | Feldspars Biotite Muscovite Ore Deposits Tin Copper Quartz Pyrite Fluorite Epidote Calcite | Mica | Monoclinic |
| Serpentine Group | Colourless | Low. 0.006-0.013 | Low Positive | Mineral group with Lizardite, Chrysotile, Antigorite/ Mesh window texture / From the alteration of Olivine | Good | Straight | Fibrous / Flakes | Uniaxial or Moderate | Negative | Igneous / Metamorphic | Calcite Hyalophane Laumontite Natrolite | Sheet | Trigonal / Monoclinic / Orthorhombic |
| Siderite | Colourless to Pale Yellow Brown | Very High | Moderate to Very High | Carbonates with the highest relief and birefringence / Simple Twinning / Length Fast | Straight | Granular / Oolitic spheres / Needles / Dendritic Aggregates / Skeletal | Uniaxial | Negative | Metamorphic (as gangue in ore body, as ore in metasomatic and hydrothermal deposits) | Analcite Calcite Phillipsite Thomsonite | Carbonate | Trigonal | |
| Sillimanite | Colourless / Rare Brown | Moderate. 0.018-0.022 up to mid 2nd order. | High | Higher briefringence and relief than Andalusite / Fibrous texture often associated with Biotite / Needles often associated with Quartz / Length Slow | Good | Straight | Fibrous (Fibrolite) or Diamond/ Needles | Small 20-30° | Positive | High T Metamorphic | Aegirine-Augite Anorthoclase Arfvedsonite Riebeckite | Al Silicate | Orthorhombic |
| Smectite Group | Colourless / Pale Brown / Yellow / Olive-Green | Moderate to High | Low | Group of Clay minerals / Fills pores / Main constituent of Bentonite | Perfect | - | Irregular Plates | - | Negative | Sedimentary | Beryl Cassiterite Wolframite Fluorite Li-Mica Quartz Tourmaline | Clay / Sheet | Monoclinic |
| Sodalite | Colourless / Pale Gray | Isotropic | Moderate Negative | Simple Twinning / Slight birefringence around inclusions | Poor | Isotropic | Anhedral to Euhedral / Cubes / Hexagonal / Corroded-looking | Isotropic | Isotropic | Igneous (Mainly alkaline volcanic) | Calcite Gypsum Halite Quartz | Sodalite (Feldspathoid) | Cubic |
| Spessartine | Pale Yellow | Isotropic | High | with Almandine | None | Isotropic | Euhedral (Rhombic Dodecahedrons; like a Hexagon with more faces) / Anhedral Grains | Isotropic | Isotropic | Metamorphic (Hornfels) / Sedimentary | Anhydrite Calcite Halite Quartz | Garnet | Cubic |
| Sphene / Titanite | Colourless to Pale Brown | Very High. 0.1-0.2 Extreme - pinky buff colours | Very High | Occurs in intermediate and acid igneous rocks / Occurs in metabasites / Low birefringence grains seldom go fully extinct, going from dull anomalous orange to dull blue | Good | Inclined 35-50° | Commonly Diamond / Lozenge shaped | Small to Moderate 17-55° | Positive | Igneous (Intermediate and Acidic, never in Gabbro or Basalts) / Metamorphic (Amphibolites, Marbles) | Celestite Quartz | Humite | Monoclinic |
| Spinel Group | Colourless / Brown / Green / Pink / Pale Blue / Never Pleochroic | Isotropic if translucent | Very High | Simple Twinning / Transparent Spinels mainly in metamorphic rocks / Colourless Spinels in marbles / Coloured Spinels in high-grade metapelites / Deep Brown, Cr-rich, Spinels in basic and ultrabasic rocks | None | Isotropic | Cubes / Octahedral | Isotropic | Isotropic | Metamorphic | Hematite Lepidocrocite | Oxide / Spinel | Cubic |
| Staurolite | Honey Yellow / Pleochroic | Low. 0.011-0.014 up to 1st order Yellow | High | Only found in metapelites / Usually as porphyroblasts with quartz inclusions / Length Slow | Moderate | Straight | Short Prisms / Tabular | Large 80-90° | Positive | Metamorphic (Metapelites) | Kyanite Garnet Mica Biotite Sillimanite | Staurolite | Monoclinic / Orthorhombic |
| Stilbite | Colourless | Very Low | Very Low | Interpenetrating Twinning | Inclined 3-12° | Radial / Fibrous / Bundled Aggregates / Skeletal / Plates | Small to Moderate 30-49° | Negative | Igneous (Cavity and Fractures Filling in basic to acidic Volcanic rocks) | Clinopyroxenes Arfvedsonite K-Feldspar Nepheline Riebeckite | Flaky Zeolite | Monoclinic | |
| Stilpnomelane | Yellow / Green / Brown / Strongly Pleochroic | High to Very High. 0.03-0.11 | Moderate to High | Cleavage less perfect than Biotite / Length Slow | Good | Straight | Elongate Prisms / Laths / Needles / Radiating / Flaky | Pseudo Uniaxial | Negative | Metamorphic (Phyllite, Schist, Quartzite, Blueschist) | Biotite Chlorite Hornblende Muscovite Quartz | Sheet | Triclinic / Monoclinic |
| Talc | Colourless to Pale Green | High. 0.037-0.050 | Moderate | Indisguishable from Sericite by microscope / Very soft clay / From the alteration of Mg Silicates / Length Slow | Perfect | Straight | Fibrous / Scaly | Small 0-30° | Negative | Metamorphic / Sedimentary | Clay / Sheet | Monoclinic | |
| Thomsonite | Colourless | Very Low | Very Low to Low | Highest birefringence of all the Zeolites / May have Simple Twinning / Renamed in 1820 in honour of Scotsman Thomas Thomson, professor of chemistry at the University of Glasgow. | Perfect | Straight | Radially / Fibrous / Columns / Elongate Prism / Flaky | Moderate to Large 44-75° | Positive | Igneous (Amygdules in basic to ultramafic magmatic rocks) / Metamorphic (Fracture filling) | Calcite Clay Minerals Quartz | Natrolite Fibrous Zeolite | Orthorhombic |
| Titanaugite | Brown / Purple / Brownish Yellow / Pleochroic | Very High | High | Hourglass texture / Zoned / Anomalous Brown to Blue-Gray at extinction/ Twinning | Good. 2 sets at 87° | Inclined 32-55° | Short to Long Columns / Platy | Moderate 42-65° | Positive | Igneous (Ti-rich alkali rocks) | Alkali-Feldspar Volcanic Glass Tridymite Zeolite | Clinopyroxene | Monoclinic |
| Titanbiotite | Orange / Red Brown | Very Low | Moderate to High | Weathered grains are bleached / Pleochroic haloes around Zircon / Occurs as fine-speckled in extinction orientation / Length Slow | Perfect | Straight (Parallel to Cleavage) | Platy / Flaky / Scaly / Columns | Small to Moderate 5-38° | Negative | Igneous (Na-rich, Ti-rich magmatic rocks) | Chlorite K-Feldspar Mica Plagioclase Quartz Rutile | Mica | Monoclinic |
| Topaz | Colourless | Very High | Moderate | Contains fluid inclusions / Length Slow / Named after Topasos Island in the Red Sea | Perfect | Straight | Short Columns / Needles / Laths / Granular | Moderate 48-68° | Positive | Metamorphic (Greisen and granitic contact metamorphism) / Igneous (Tin pegmatites) | Apatite Calcite Diopside Vesuvianite Wollastonite Quartz Mica Feldspar Fluorite Cassiterite Tourmaline | Orthorhombic | |
| Tourmaline | Opaque / Blue / Green / Yellow / Brown / Strongly Pleochroic | Moderate. 0.02-0.03 up to up 2nd order. | Moderate | Pleochroism darkest when N-S / Often colour zoned / Radioactive haloes around Zircon / Good indication that the rock is Boron rich / Distinguished from biotite and hornblende by the lack of cleavage / Length Fast | Poor | Straight | Triangular / Prisms / Needle-like | Uniaxial | Negative | Igneous / Metamorphic | Topaz | Epidote | Trigonal |
| Tremolite | Colourless to Green Pleochroic | Moderate. 0.027 up to mid 2nd | Moderate | Colour more intense for Fe-rich Tremolites / Only found in carbonate-rich metamorphic rocks (e.g. marbles) / May have pleochroic haloes / Length Slow | Good. 2 sets at 124° | Inclined 30° max typically 10-15° | Fine Prisms / Laths / Fibrous / Needle-like | Large 80-90° | Negative | Metamorphic (Green and Blueschist, Serpentinite, Marbles) | Apatite Calcite Phlogopite | Actinolite Amphibole | Monoclinic |
| Tridymite | Colourless | Very Low. 0.002-0.004 | Moderate Negative | Lines vesicles in high temperature lavas / High temperature polymorph of Quartz / Occurs in volcanic rocks / Fracture Filling / Twinning / Length Fast | Poor | Straight | Radiating Rays / Platy | Moderate to Large 40-90° | Positive | Igneous (Volcanic) Metamorphic (Sanidine facies contact met.) | Framework SiO2 | Orthorhombic | |
| Tschermakite Group | Bright Green to Yellow Green / Pleochroic | Very High | Moderate to High | May have pleochroic haloes / Use associated minerals to distinguish from other amphiboles / Alters to Actinolite, Antigorite, Chlorite / Length Slow | Inclined 15-22° | Short to Long Columns / Needles | Moderate to Large 65-90° | Negative | Igneous (Intermediate to acidic rocks and Lamprophyrs) / Metamorphic (Amphibolite and Amphibole Schists) | Clinopyroxenes Leucite Nepheline Sanidine Sodalites | Green Hornblende Amphibole | Monoclinic | |
| Uvarovite | Pale "Emerald" Green | Isotropic (may be anomalous) | Very High | Zonal growth rings / Mottled colour texture | None | Isotropic | Euhedral (Rhombic Dodecahedrons; like a Hexagon with more faces) / Anhedral Grains | Isotropic | Isotropic | Found in Chromite rich rocks | Tridymite Zeolite | Garnet | Cubic |
| Vesuvianite / Idocrase | Colourless / Yellow / Green / Brown / Weakly Pleochroic | Low / May be anomalous Purple Blue or Leather Brown | High | May have zoned colour distribution / Hourglass texture | Poor | Straight | Short Prisms / Granular / Needles / Spherulitic | Uniaxial | Positive / Negative | Metamorphic (Contact metamorphism and marbles) | Olivine Serpentine | Tetragonal | |
| Volcanic Glass | Colourless / Yellow to Brown | Opaque / Anomalous | Very Low to Moderate | Fluid textures / Contraction and Conchoidal fractures / Radial devitrification textures | Amorphous | Igneous (Volcanic rocks, dykes and sills) | Carbonates Serpentine | - | - | ||||
| Wollastonite | Colourless | Low. 0.013 | Moderate | Refractive index < Diopside / Twinning / Poikiloblastic | Good. 3 sets at 84 and 70° | Inclined 30-40° | Prisms / Hexagonal / Needles | Moderate 35-60° | Negative | Metamorphic (Marbles) | Technically not a Pyroxene | Triclinic | |
| Xenotime | Colourless / Yellow / Green / Red / Weakly Pleochroic | Very High | High | May have Pleochroic haloes / Length Slow | Good | Straight | Short Prisms / Granular | Uniaxial | Positive | Igneous (Felsic rocks) / Metamorphic (Orthogneiss) / Sedimentary (Sandstones) | Phosphate | Tetragonal | |
| Zeolite Group | Colourless | Low (1st order White) | Low to Moderate Negative | Cavity filling in volcanic rocks | - | - | - | Uniaxial or Biaxial | Positive or Negative | Igneous | Olivine Phlogopite Pyroxene Serpentine | Feldspathoid | - |
| Zinnwaldite | Colourless to Brown-grey / Weakly Blue Gray Pleochroic | Very High | Low to Moderate | Occurs as fine-speckled in extinction orientation / Length Slow | Perfect | Straight (Parallel to Cleavage) | Fan Shaped / Radiating / Platy / Flaky / Scaly / Columns | Small to Moderate 15-32° | Negative | Igneous (Granite Pegmatites) / Metamorphic (Greisen) | Cassiterite Clino And Ortho Pyroxene Ilmenite Magnetite Olivine Plagioclase | Lithionite Series Mica | Monoclinic |
| Zircon | Colourless to Pale Brown / Greenish or Pink / Weak or No Pleochroism | High. 0.04-0.065 up to 3rd order | Very High | Often within biotite / May have pleochroic haloes / May be zoned / Rich in inclusions / Occurs as rare detrital grains in Quartzites and mature sedimentary rocks / Length Slow | Poor | Straight | Prisms / Cubes / Small Euhedral crystals | Uniaxial | Positive | Igneous (often in nepheline syenites) / Metamorphic / Sedimentary | Humite | Tetragonal | |
| Zoisite / Thulite | Colourless / Purple / Strongly Pleochroic | Very Low / Anomalous Blue to Brown | Moderate | Length Fast | Good. 2 sets | Straight | Prisms | Uniaxial | Positive | Metamorphic (Low Grade) | Epidote | Orthorhombic |