Term
Diamond C Native
Cxl: ISO Octahedral most common, also cubes and dodecahedrons. Sometimes in rounded forms. Perfect {111} octahedral cleavage.
Color: Pale yellow or colorless most common, several other colors
H: 10 G: 3.52
Characteristics: Hardness, adamantine luster, high index of refraction. Thermal conductivity 4X that of copper, electrical insulator.
Similar Minerals: No similar natural materials
Environments: Source from kimberlites-ultramafic, potassic rocks with deep mantle sources. Also found in alluvial deposits.
Uses: Gem, abrasive, surgical knives
Comments: Polymorph of carbon |
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Definition
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Term
Graphite C Native
Cxl: HEX Tabular hexagonal plates, also massive and crystal aggregates. Perfect {0001} cleavage (sheets)
Color: Black
H: 1-2 G: 2.23
Characteristics: Black color, foliated, greasy feel. Electrical conductor.
Similar Minerals: molybdenite, but black, not blue streak
Environments: Marbles, schists and gneisses or hydrothermal veins as at Ticonderoga, NY. Indicates reducing environments.
Uses: Lubricant, refractory crucibles. Most graphite is synthetically produced.
Comments: Pencil “lead” is actually graphite |
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Definition
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Term
Gold Au Native
Cxl: ISO Octhedra, arborescent groups
Color: Yellow
H: 2.5-3 G: 19.3 (Pb=11.3)
Characteristics: Sectile, malleable, and ductile. Untarnished yellow color, low hardness. Excellent electrical conductor. Chemically unreactive.
Similar Minerals: Pyrite, chalcopyrite, altered micas
Environments: Hydrothermal veins (lodes) with quartz, placers, colloidal trace element deposits
Uses: Contacts, wire, etc. Malleable, 1oz Au=100sf sheet; ductile 1 oz = 5 mile wire!
Comments: Fineness = ppt; Karat = parts/24. Most gold contains some silver in solid solution. |
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Definition
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Term
Copper Cu Native
Cxl: ISO Irregular masses, plates, dendrites
Color: Red/tarnished
H: 2.5-3 G: 8.9
Characteristics: Sectile, ductile, malleable
Environments: Hydrothermal alteration of basic lavas, e.g. Keweenaw Peninsula, MI
Uses: Minor ore of Cu |
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Definition
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Term
Silver Ag Native
Cxl: ISO Irregular plates, masses, arborescent groups, "wire"
Color: Silver white on fresh surfaces, but typically tarnished black
H: 2.5-3 G: 10.5
Characteristics: Malleable, color on fresh surface
Environments: Hydrothermal deposits and as a secondary mineral after silver sulfides
Uses: Jewelry, brazing alloys, photoemulsions
Comments: Use in coinage now largely over. Origin of Dollar-German silver coin called the Thaler. |
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Definition
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Term
Sulfur S Native
Cxl: ORT Dipyramidal cxls, massive and encrustations
Color: Yellow
H: 1.5-2.5 G: 2.05-2.09
Characteristics: Yellow color, burns in candle flame, no cleavage
Similar Minerals: Orpiment, but lacks cleavage
Environments: Volcanic fumaroles, cap rock of salt domes in Gulf Coast
Uses: Sulfur compounds, vulcanizing rubber, fertilizers
Comments: One of the few rocks that burns! Can light it with a match. |
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Definition
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Term
Galena PbS Sulfides
Cxl: ISO Cxls common as cube, cube truncated by octahedron
Color: Lead gray, metallic luster, streak same color
H: 2.5 G: 7.4-7.6
Characteristics: Color, perf cubic cleavage {001}, high G
Similar Minerals: Molybdenite and Stibnite are similar in color and luster, but lack cubic cleavage.
Environments: Hydrothermal veins with silver, gold. With Zn in massive deposits—black smokers
Uses: Important ore of Pb, but also silver
Comments: relatively common mineral in small amounts |
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Definition
Galena and Quartz
(M1501) (M1627) |
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Term
Molybdenite MoS2 Sulfides
Cxl: HEX Crystals as hexagonal plates, commonly foliated masses
Color: Lead-gray with bluish tones
H: 1-1.5 G: 4.6-4.7
Characteristics: Color, low hardness, perf {0001} sheet like cleavage, foliated form
Similar Minerals: Looks like graphite but blue tint, streak is greenish, not black like graphite.
Environments: Moly porphyries, assoc with Cu porphyries; also a high T vein mineral with cassiterite, scheelite and wolframite
Uses: Principal ore of molybdenum
Comments: Moly is an important alloying element in steels, provides toughness |
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Definition
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Term
Sphalerite ZnS Sulfides
Cxl: ISO Usually massive or in distorted, twinned cxls. Tetrahedron, doedecahedron and cube common
Color: Colorless to yellow to black. Darker with more Fe. Distinctive resinous luster.
H: 3.5-4 G: 3.9-4.1
Characteristics: Resinous luster and perfect {011} cleavage (more than 3 directions!)
Environments: Common mineral, wide range of environments but most deposits are hydrothermal
Uses: Ore of Zn
Comments: Primary ore of zinc. “Galvanized” metal—zinc coating on steel to prevent rusting. Older literature may call sphalerite “zinc blende”. Some Fe can substitute for Zn, “black jack” ore. |
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Definition
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Term
Cinnabar HgS Sulfides
Cxl: HEX Rarely in cxls, usually massive; 1 perf cleavage {10 -10}
Color: Vermillion red Luster: adamantine on fresh surfaces, otherwise dull
H: 2.5 G: 8.1 Streak: scarlet red
Characteristics: color, cleavage
Environments: Spring deposits, low T hydrothermal veins Uses: Chief ore of Hg
Comments: Famous deposits in Almaden, Spain. Used in gold refining, dental amalgams, old electrical switches. Hg is a toxic metal, bioaccumulates particularly in fish. |
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Definition
Cinnabar
(M304, 373, 382, 417) |
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Term
Orpiment As2S3 Sulfides
Cxl: MON Cxls rare, small tabular or prismatic. More common in foliated masses. Cleavage: {010} perfect, flexible flakes. Sectile.
Color: Lemon yellow, resinous luster. Streak pale yellow.
H: 1.5-2 G: 3.49
Characteristics: Yellow color, foliated character distinguishes it from sulfur. Associated with realgar.
Similar Minerals: Sulfur
Environments: Fumaroles and hot springs--associated with realgar
Uses: Tanning of hides, formerly a pigment |
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Definition
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Term
Realgar AsS Sulfides
Cxl: MON Short, vertically striated prismatic cxls. Commonly granular, massive. Cleavage: {010} good
Color: Red to orange, resinous luster, red to orange streak.
H: 1.5-2 G: 3.5
Characteristics: Red color, resinous luster and typically
associated with yellow orpiment
Similar Minerals: Cinnabar--but color is more orange vs deep red of cinnabar; realgar usually associated with orpiment
Environments: Occurs with orpiment in fumaroles, hot springs; found with Au, Pb, Ag veins.
Uses: Was used as a pigment, color agent in fireworks-brilliant white light |
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Definition
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Term
Stibnite Sb2S3 Sulfides
Cxl: ORT Slender prismatic, elongated and striated || c. Often in bladed or radiating cxls. Cleavage: {010} perfect in planes parallel long axis of bladed cxls
Color: Lead gray, metallic luster, lead gray streak.
H: 2 G: 4.5-4.6
Characteristics: Color, luster, bladed habit, perfect cleavage,
fuses in candle flame
Similar Minerals: Not much--galena, molbydenite, graphite but different habits, cleavage
Environments: Low temp hydorthermal veins and hot springs Uses: Ore of antimony, pigment and in glass making |
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Definition
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Term
Chalcopyrite CuFeS2 Sulfides
Cxl: TET Usually massive, also as tetrahedral cxls
Color: Brass yellow, metallic luster. Greenish-black streak.
H: 3.5-4 G: 4.1-4.3
Characteristics: Color, streak, iridescent tarnish
Similar Minerals: Like pyrite like, but color more yellow, tarnish. Cu-bearing
Environments: Hydrothermal veins and disseminated in porphyry copper deposits
Uses: Cu ore
Comments: Main ore of Cu in Cu porphyries. |
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Definition
Chalcopyrite
(M389, M212, M198) |
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Term
Chalcocite Cu2S Sulfides
Cxl: MON Habit: Cxls uncommon, usually massive. Cxls small and tabular with hex outline-hexagonal above 105°C. Striated || a
Imperfect {110} cleavage, rarely observed
Color: Metallic lead gray on fresh surface, weathers black; gray-black streak.
H: 2.5-3 G: 5.5-5.8
Characteristics: Metallic luster, imperfectly sectile, may appear sooty
Environments: Can be a vein mineral, but most important in supergene enriched zone just below WT of Cu deposits.
Uses: Copper ore |
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Definition
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Term
Covellite CuS Sulfides
Cxl: HEX Habit: Usually massive, tabular cxls rare Perfect {0001} cleavage mica like, flexible sheets
Color: Indigo blue with metallic luster , lead gray to black streak.
H: 1.5-2 G: 4.6-4.8
Characteristics: Metallic luster and blue color, cleavage Environments: Supergene Cu mineral in oxidized parts of
weathering profiles.
Uses: Cu ore |
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Definition
Covellite
(M14, M389, M418, M1583) |
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Term
Pyrite FeS2 Sulfides
Cxl: ISO Cube with striated faces, pyritohedron, octahedron. Commonly penetratively twinned
Color: Pale yellow, metallic luster; green to brownish black streak
H: 6-6.5 !!! G: 5 Conchoidal fracture.
Characteristics: Color and high hardness, no cleavage, fracture
Similar Minerals: Marcasite which is lighter colored and has
different cxl form, chalcopyrite which contains copper
Environments: Most common sulfide--found in nearly every environment!
Uses: Was mined for sulfuric acid production, declining. May be Au or Cu ore—inclusions of native elements.
Comments: Alters readily to Fe oxides/hydroxides, sometimes pseudomorphs. Lack of pyrite an important characteristic of good dimension stone. Fine grained pyrite in sediments can be black. |
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Definition
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Term
Marcasite FeS2 Sulfides
Cxl: ORT Cxls tabular on {010}, Twinned to give cockscomb and spear shaped groups, radiating structures.
Color: Pale yellow color Luster: Metallic on fresh sufraces Streak: gray-black
H: 6-6.5 !!!, softer where weathered! G: 4.9
Characteristics: Rounded forms, disintegrates to a white, powdery Fe sulfate.
Similar Minerals: pyrite
Environments: Metalliferous veins with Pb and Zn ores, concretions in clays, marls and shales
Uses: minor source for sulfur Comments: Low temp polymorph of FeS2 |
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Definition
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Term
Pyrrhotite Fe(1-x)S Sulfides
Cxl: MON Tabular hexagonal crystals rare, typically massive aggregates. Hexagonal at high temps.
Color: Brownish bronze , metallic luster
H: 4 G: 4.6
Characteristics: Massive, bronze color and magnetic, but varies with Fe, higher Fe = less magnetic
Similar Minerals: Pentlandite, but magnetic and no parting as in pentlandite
Environments: Common in basic igneous rocks, norites, magmatic segregation
Comments: Important constitutent of Sudbury ores. Note omission
solid solution. |
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Definition
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Term
Pentlandite (Fe,Ni)9S8 Sulfides
Cxl: ISO Massive, granular aggregates w/ octahedral parting on {1 1 1}
Color: Yellowish bronze, metallic luster
H: 3.5-4 G: 4.6-5
Characteristics: Bronze color and octahedral parting
Similar Minerals: Pyrrhotite, but parting and nonmagnetic Environments: Common in basic igneous rocks as a magmatic
segregation
Uses: Principal ore of Ni. Ni alloys have greater strength and toughness, important constituent of stainless steels
Comments: Note Fe-Ni solid solution. Major occurrence at Sudbury, Ontario |
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Definition
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Term
Hematite Fe2O3 Oxides
Cxl: HEX Tabular on {0001}, plates may be grouped as rosettes. Also foliated masses (specularite) and red-brown aggregates--oolitic. No cleavage, but may show nearly cubic parting
Color: Reddish brown to black or grey, red brown streak.
H: 5.5-6.5 G: 5.3
Characteristics: Metallic luster in specularite, red brown streak
Similar Minerals: Earthy samples might be confused with goethite, but deeper red color.
Environments: Common in all rock types. Major iron deposits are Banded Fe Formations--hematite interlayered with red cherts--restricted to preCambrian.
Uses: Most important ore of iron for cast iron and steels.
Comments: Fe in hematite is oxidized--the +3 valence state. Can be deposited when Fe oxidizes--reduced Fe is more soluble and mobile. Important pigment in rocks. |
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Definition
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Term
Corundum Al2O3 Oxides
Cxl: HEX Tabular on {0001} or prismatic; rounded barrel shapes with horizontally striated faces
Color: Usually brown, pink or blue, but highly variable in color, e.g. ruby
H: 9 G: 4
Characteristics: Shape and hardness--be careful to test fresh surfaces! Parting on {0001} and {10-11}.
Environments: High grade metamorphic rocks and silica deficient igneous rocks.
Uses: Gemstones-red is ruby, blue and green are sapphires. Star sapphires have hexagonal pattern of inclusions. Important abrasive- black emery.
Comments: Hematite group. Grown synthetically for both abrasives and gem stones. |
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Definition
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Term
Ilmenite FeTiO3 Oxides
Cxl: HEX Crystals as thick tabular plates, but uncommon. Usually massive, compact. Also as detrital grains in sands.
Color: black , submetallic luster
H: 5.5-6 G: 4.7
Characteristics: Black to brown-red streak, weakly magnetic. Similar Minerals: Perovskite, CaTiO3 in silica poor rocks. Environments: Usually an accessory mineral in igneous rocks. Can become concentrated in placer sands.
Uses: Major ore of Ti for use in pigments, light weight and corrosion resistant metal.
Comments: Sand mines on N. Stradbroke Island, Qld, AU |
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Definition
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Term
Chromite FeCr2O4 Oxides
Cxl: ISO Cxls rare, commonly massive, granular, no cleavage Color: Black to brownish black, submetallic luster. Black-brown streak. H: 5.5 G: 4.6 Characteristics: Pitchy luster on fresh broken surfaces, occurrence Similar Minerals: magnetite, ilmenite but chromite is not magentic;
ulvospinel, Fe2TiO4
Environments: Peridotites, ultrabasic igneous rocks, serpentinites; magmatic segregation deposits.
Uses: Only ore of Chromium
Comments:Also used as a refractory material. Mg can substitute for Fe |
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Definition
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Term
Hematite Fe2O3 Oxides
Cxl: HEX Tabular on {0001}, plates may be grouped as rosettes. Also foliated masses (specularite) and red-brown aggregates--oolitic. No cleavage, but may show nearly cubic parting
Color: Reddish brown to black or grey, red brown streak.
H: 5.5-6.5 G: 5.3
Characteristics: Metallic luster in specularite, red brown streak
Similar Minerals: Earthy samples might be confused with goethite, but deeper red color.
Environments: Common in all rock types. Major iron deposits are Banded Fe Formations--hematite interlayered with red cherts--restricted to preCambrian.
Uses: Most important ore of iron for cast iron and steels.
Comments: Fe in hematite is oxidized--the +3 valence state. Can be deposited when Fe oxidizes--reduced Fe is more soluble and mobile. Important pigment in rocks. |
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Definition
Hematite
(M426),(M23,M28,M342) |
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Term
Corundum Al2O3 Oxides
Cxl: HEX Tabular on {0001} or prismatic; rounded barrel shapes with horizontally striated faces
Color: Usually brown, pink or blue, but highly variable in color, e.g. ruby
H: 9 G: 4
Characteristics: Shape and hardness--be careful to test fresh surfaces! Parting on {0001} and {10-11}.
Environments: High grade metamorphic rocks and silica deficient igneous rocks.
Uses: Gemstones-red is ruby, blue and green are sapphires. Star sapphires have hexagonal pattern of inclusions. Important abrasive- black emery.
Comments: Hematite group. Grown synthetically for both abrasives and gem stones. |
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Definition
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Term
Ilmenite FeTiO3 Oxides
Cxl: HEX Crystals as thick tabular plates, but uncommon. Usually massive, compact. Also as detrital grains in sands.
Color: black , submetallic luster
H: 5.5-6 G: 4.7
Characteristics: Black to brown-red streak, weakly magnetic. Similar Minerals: Perovskite, CaTiO3 in silica poor rocks. Environments: Usually an accessory mineral in igneous rocks. Can become concentrated in placer sands.
Uses: Major ore of Ti for use in pigments, light weight and corrosion resistant metal.
Comments: Sand mines on N. Stradbroke Island, Qld, AU |
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Definition
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Term
Chromite FeCr2O4 Oxides
Cxl: ISO Cxls rare, commonly massive, granular, no cleavage Color: Black to brownish black, submetallic luster. Black-brown streak. H: 5.5 G: 4.6 Characteristics: Pitchy luster on fresh broken surfaces, occurrence Similar Minerals: magnetite, ilmenite but chromite is not magentic;
ulvospinel, Fe2TiO4
Environments: Peridotites, ultrabasic igneous rocks, serpentinites; magmatic segregation deposits.
Uses: Only ore of Chromium
Comments:Also used as a refractory material. Mg can substitute for Fe |
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Definition
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Term
Cassiterite SnO2 Oxides
Cxl: TET Prismatic with dipyramidal terminations. Can be twinned--visor tin with {011} composition plane. Also in reniform masses with radiating fibrous appearance. Imperfect {010} cleavage.
Color: Brown or black, rarely lighter colors, white streak. Adamantine to submetallic luster
H: 6-7 G: 6.8-7.1
Characteristics: High SG, white streak, luster, cxl form, imperf cleavage
Similar Minerals: Rutile, but rutile has lower SG
Environments: High temperature veins near granitic rocks. Placer deposits of alluvial tins.
Uses: Chief ore of tin.
Comments: Tin is used as a coating in tin cans, as an alloy with Pb in solders, and with Cu in bronze. |
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Definition
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Term
Rutile TiO2 Oxides
Cxl: TET Typically in prisms with dipyramid terminations, vertically striated prism faces. Often in elbow, cyclic twins with {011} composition plane. Distinct {110} cleavage.
Color: Reddish brown, adamantine luster
H: 6-6.5 G: 4.2
Characteristics: Red color, luster, twins
Similar Minerals: Can look like cassiterite, but lower G. Environments: Granites and granite pegmatites, also metamorphic rocks. Placer deposits.
Uses: Ore of Ti, strong lightweight metal components: coating for welding rods, pigments, sun blocks. |
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Definition
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Term
Bauxite Al-hydroxides Oxides
Cxl: NA Massive, pisolitic
Color: White, tan, brown, typically Fe-stained
H: 1-3 G: 2-2.5
Characteristics: Earthy, nodular masses.
Environments: Really a rock--supergene weathering of low-Si rocks. A mixture of the Al hydroxides diaspore, gibbsite, boehmite
Uses: Chief ore of aluminum
Comments: Not really a mineral, but a rock. Most deposits found in tropics-- areas of high rainfall. Refined electrolytic ally. One of the few ores that is transported to refining sites, not refined at the mine. |
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Definition
Bauxite
(M391, M368, M385) |
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Term
Geothite αFeO(OH) Oxides
Cxl: ORT Rarely in prismatic crystals, acicular crystals, radiating masses, stalactitic. Reniform to botryoidal masses. Cleavage {010} perfect
Color: Dark brown almost black to orange-brown. Highly variable streak- admantine, silky, or dull. Brown streak.
H: 5-5.5 G: 4.4
Characteristics: Brown streak (not reddish like hematite) Similar Minerals: Lepidocrocite, another Fe hydroxide polymorph
Environments: Formed under oxidizing conditions as a weathering product of Fe-bearing minerals
Uses: An ore of Fe
Comments: Bog-iron; Limonite is a field term for mixed Fe-hydroxides. Important coloring agent in some soils, rocks. |
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Definition
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Term
Magnetite Fe3O4 Oxides
Cxl: ISO Octahedral crystals {1 1 1} , granular masses, usually equant grain shapes
Color: Black, metallic to submetallic luster, black streak
H: 6 G: 5.2
Characteristics: Magnetic! May be naturally magnetized = lodestone
Similar Minerals: Ilmenite can be weakly magnetic Environments: Common accessory mineral in igneous rocks. Also found in metamorphic rocks, placers.
Uses: An ore of iron
Comments: Contains both Fe2+ and Fe3+. Fe2+ in ss with Ti,
ulvospinel. |
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Definition
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