Rocks and Minerals/Identification List

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This is a compilation of information for the event Rocks and Minerals. Please note that while this is a good starting resource, it should not be relied on. There are many more facts about Rocks and Minerals that are not included. Please make your own fact sheets.

Rocks

Metamorphic

Gneiss (60)

Picture Gneiss.jpg
Classification Metamorphic
Composition Light bands: Quartz, Feldspar, Muscovite, Dark bands: Hornblende, Biotite, Graphite, Garnet
Environment of Formation High-grade metamorphism of Granite
Texture Foliated
Economic Importance Flooring, ornamental stones, gravestones, facing stones on buildings, work surfaces
Average Density 2.6-2.9

Marble (61)

Picture Marble.jpg
Classification Metamorphic
Composition Mainly metamorphosed limestone (CaCO3)
Environment of Formation High-grade metamorphism of Limestone
Texture Nonfoliated
Economic Importance Ornamental rock, sculpture production, urban ornamentation
Average Density 2.4-2.7

Phyllite (62)

Picture Phyllite.jpg
Classification Metamorphic
Composition Quartz, Sericite Mica, Chlorite
Environment of Formation Medium-grade metamorphism of Slate
Texture Foliated
Economic Importance Architecture, construction, commercial
Average Density 2.7-2.8

Quartzite (63)

Picture Quartzite.jpg
Classification Metamorphic
Composition Almost entirely Quartz
Environment of Formation High-grade metamorphism of Sandstone
Texture Nonfoliated
Economic Importance Railway ballast, countertops, decorative stone
Average Density 2.6-2.8


Garnet Schist (64)

Picture Garnet Schist.jpg
Classification Metamorphic
Composition Muscovite, Biotite, Garnet, Quartz, Feldspar
Environment of Formation Medium grade metamorphism of Shale, Mudstone, or Felsic Igneous rocks
Texture Foliated
Economic Importance Gem material host rock, construction material (rarely)
Average Density 2.4-3.0

Mica Schist (65)

Picture Mica Schist.jpg
Classification Metamorphic
Composition Muscovite, Biotite, Garnet, Quartz, Feldspar
Environment of Formation Medium grade metamorphism of Shale, Mudstone, or Felsic Igneous rocks
Texture Foliated
Economic Importance Gem material host rock, construction material (rarely)
Average Density 2.4-3.0

Slate (66)

Picture Slate.jpg
Classification Metamorphic
Composition Mainly Quartz and Muscovite
Environment of Formation Low-grade metamorphism of Shale
Texture Foliated
Economic Importance roofing, flooring, flagging
Average Density 2.7-2.8


Igneous

Andesite (67)

Picture Andesite.jpg
Classification Igneous
Composition Intermediate (Plagioclase Feldspar, Biotite, Pyroxene, Amphibole)
Environment of Formation Extrusive, Volcanic
Texture Aphanitic to Porphyritic
Economic Importance Aggregate, construction
Average Density 2.5-2.8

Basalt (68)

Picture Basalt.jpg
Classification Igneous
Composition Mafic (Plagioclase and Pyroxene minerals)
Environment of Formation Extrusive, Volcanic
Texture Aphanitic
Economic Importance Aggregate, pavement, ballast
Average Density 2.8-3.0

Diorite (69)

Picture Diorite.jpg
Classification Igneous
Composition Intermediate (Plagioclase Feldspar, Biotite, Pyroxene, Amphibole)
Environment of Formation Intrusive, Plutonic
Texture Phaneritic
Economic Importance Construction stone, sculpture stone, architectural stone
Average Density 2.8-3.0

Gabbro (70)

Picture
Gabbro
Classification Igneous
Composition Mafic (Pyroxene, Plagioclase, minor amounts of Amphibole and Olivine)
Environment of Formation Intrusive, Plutonic
Texture Phaneritic
Economic Importance Ornamental stone, countertops, graveyard headstones
Average Density 2.7-3.3

Granite (71)

Picture Granite.jpg
Classification Igneous
Composition Felsic (Quartz, Alkali Feldspar, Plagioclase Feldspar)
Environment of Formation Intrusive, Plutonic
Texture Phaneritic
Economic Importance Buildings, bridges, paving, monuments, countertops, ornamental stone
Average Density 2.6-2.7

Obsidian (72)

Picture Obsidian.jpg
Classification Igneous
Composition Felsic (Mostly Silica)
Environment of Formation Extrusive
Texture Glassy
Economic Importance Weapons and tools (Stone Age)
Average Density 2.3-2.6

Pegmatite (73)

Picture Pegmatite.jpg
Classification Igneous
Composition Felsic (Granite)
Environment of Formation Intrusive, Plutonic
Texture Phaneritic
Economic Importance Host rock for rare minerals
Average Density 2.6-2.8

Pumice (74)

Picture Pumice.jpg
Classification Igneous
Composition Felsic (Rhyolite)
Environment of Formation Extrusive, Volcanic
Texture Vesicular
Economic Importance Aggregate, abrasive
Average Density 0.2-0.3

Rhyolite (75)

Picture Rhyolite.jpg
Classification Igneous
Composition Felsic (Quartz, Sanidine, Plagioclase)
Environment of Formation Extrusive, Volcanic
Texture Aphanitic
Economic Importance Cements
Average Density 2.4-2.6

Scoria (76)

Picture Scoria.jpg
Classification Igneous
Composition Mafic (Basalt)
Environment of Formation Extrusive, Volcanic
Texture Vesicular
Economic Importance Landscaping, drainage, barbecue grills
Average Density Greater than 1


Sedimentary

Arkose (78)

Picture Arkose.jpg
Classification Sedimentary
Composition Feldspar, Quartz, Mica
Environment of Formation Weathering of Feldspar rich Igneous and Metamorphic Rocks
Texture Clastic
Economic Importance Ornaments, building, molars
Average Density 2.2-2.8

Breccia (80)

Picture Breccia.jpg
Classification Sedimentary
Composition Quartz, Feldspar, Mica, Calcite, Clay
Environment of Formation Where broken, angular fragments of rock or mineral debris accumulate
Texture Clastic
Economic Importance Sculptures, road beds, statues
Average Density 2.0-2.4

Chert (81)

Picture Chert.jpg
Classification Sedimentary
Composition Silicon Dioxide
Environment of Formation Deep marine, thin beds
Texture Chemical
Economic Importance Weapon, tools (past)
Average Density 2.4-2.6

Conglomerate (82)

Picture Conglomerate.jpg
Classification Sedimentary
Composition Mineral particles such as Quartz or Feldspar, can be Sedimentary, Metamorphic, or Igneous rock fragments
Environment of Formation Along a swiftly flowing stream or a beach with strong waves that carry and weather clasts
Texture Clastic
Economic Importance Construction industry
Average Density 2.4-2.6

Diatomite (83)

Picture Diatomite.jpg
Classification Sedimentary
Composition Diatomaceous Earth (Diatoms)
Environment of Formation Shallow-marine environments
Texture Organic
Economic Importance Filter, absorbent, pest control
Average Density 1.6-1.8

Dolostone (85)

Picture Dolostone.jpg
Classification Sedimentary
Composition Dolomite mineral
Environment of Formation Limestone marine deposits on ancient shallow seafloors
Texture Chemical
Economic Importance Acid neutralization, construction, source of Magnesium
Average Density 2.8-9

Sandstone (92)

Picture Sandstone.jpg
Classification Sedimentary
Composition Quartz, Feldspar
Environment of Formation Depositional environments
Texture Clastic
Economic Importance Buildings, monuments, grave stones, silica for glass
Average Density 2.2-2.8

Shale (95)

Picture Shale.jpg
Classification Sedimentary
Composition Mud that is a mix of flakes of clay minerals and tiny fragments of other minerals
Environment of Formation Marine environments; silt or mud is deposited in calm waters
Texture Clastic
Economic Importance Additive in cement, art clay products
Average Density 2.4-2.8


Coal Varieties

Anthracite (77)

Picture Anthracite.jpg
Classification Sedimentary (Coal)
Composition Carbon (87%)
Environment of Formation Heat and pressure, from Bituminous
Texture Organic
Economic Importance Coal
Average Density 1.1-1.4

Bituminous (79)

Picture Bituminous.jpg
Classification Sedimentary (Coal)
Composition Carbon (60-80%)
Environment of Formation Organic Metamorphism
Texture Organic
Economic Importance Coal
Average Density 1.1-1.4

Lignite (86)

Picture Lignite.jpg
Classification Sedimentary (Coal)
Composition Carbon (60-70%)
Environment of Formation Transformed Peat
Texture Organic
Economic Importance Coal
Average Density 1.1-1.4


Limestone Varieties

Chalk (87)

Picture Chalk.jpg
Classification Sedimentary (Limestone)
Composition Calcium Carbonate
Environment of Formation Deep marine conditions
Texture Chemical
Economic Importance Raising pH in soil with low pH, antacid, cleaning
Average Density 2.3-2.7

Coquina (83)

Picture Coquina.jpg
Classification Sedimentary (Limestone)
Composition Calcium Carbonate/Shells
Environment of Formation Near-shore environments
Texture Chemical
Economic Importance Paving material, fertilizer
Average Density 2.3-2.7

Fossiliferous (89)

Picture Fossiliferous.jpg
Classification Sedimentary (Limestone)
Composition Calcium Carbonate with fossil imprints
Environment of Formation Shallow marine waters
Texture Chemical
Economic Importance Geologic clues, ornaments, jewelry
Average Density 2.3-2.7

Oolitic (90)

Picture Oolitic.jpg
Classification Sedimentary (Limestone)
Composition Calcium Carbonate
Environment of Formation Warm, supersaturated marine water
Texture Chemical
Economic Importance Ornaments, limestone
Average Density 2.3-2.7

Travertine (91)

Picture Travertine.jpg
Classification Sedimentary (Limestone)
Composition Calcium Carbonate
Environment of Formation Precipitation of Carbonate minerals from solution in ground and surface waters
Texture Chemical
Economic Importance Countertops, building material
Average Density 2.3-2.7


Minerals

Borates

Ulexite (59)

Picture
Ulexite
Classification Borate
Chemical Composition NaCa[B5O6(OH)6] · 5H2O
Hardness 2.5
Streak White
Luster Vitreous, silky
Cleavage Prismatic, basal
Fracture Splintery
Density 1.955 g/cm3
Mineral Habit Articular, capillary, fibrous
Crystal System Triclinic, pinacoidal
Environment of Formation Borax evaporite deposits in dry lakes of arid regions
Economic Importance The boron in it is mainly used for fiberglass

Carbonates

Aragonite (5)

Picture
Aragonite
Classification Carbonate
Chemical Composition CaCo3
Hardness 3.5-4
Streak White
Luster Vitreous
Cleavage Prismatic, indiscernible
Fracture Subconchoidal
Density 2.947 g/cm3
Mineral Habit Columnar, fibrous, pseudohexagonal
Crystal System Orthorhombic
Environment of Formation Sedimentary formations and evaporite deposits, hot spring deposits, hydrothermal ore veins, igneous environments, and metamorphic schists.
Economic Importance Used as specimens

Azurite (7)

Picture
Azurite
Classification Carbonate
Chemical Composition Cu3(CO3)2(OH)2
Hardness 3.5-4
Streak Light blue
Luster Vitreous
Cleavage Perfect, fair
Fracture Conchoidal or splintery
Density 3.77 g/cm3
Mineral Habit Prismatic, stalactitic, tabular
Crystal System Monoclinic
Environment of Formation Reaction from carbon-dioxide laden waters descending into the earth and reacting with subsurface copper ores
Economic Importance Jewelry, pigment, an indicator for subsurface copper ores

Calcite (13)

Picture
Calcite
Classification Carbonate
Chemical Composition CaCO3
Hardness 3
Streak White
Luster Vitreous
Cleavage Rhombohedral
Fracture Conchoidal
Density 2.7102 g/cm³
Mineral Habit Crystalline, massive, stalactitic
Crystal System Trigonal
Environment of Formation Forms in all rock types
Economic Importance Used in acid neutralization, as a low-hardness abrasive, soil conditioner, heated for the production of limestone and marble, and in monuments and calcium carbonate sorbents.

Dolomite (19)

Picture
Dolomite
Classification Carbonate
Chemical Composition CaMg(CO3)2
Hardness 3.5-4
Streak White
Luster Vitreous, pearly
Cleavage Rhombohedral
Fracture Subconchoidal
Density 2.84 - 2.86 g/cm3
Mineral Habit Blocky, crystalline, massive
Crystal System Hexagonal
Environment of Formation In sedimentary rock; occasionally in high-temperature metamorphic rocks and low-temperature hydrothermal veins.
Economic Importance Used in road construction, as an acid neutralizer, a source of magnesia (MgO), a feed additive for livestock, as an ingredient in the production of glass, bricks, and ceramics.

Malachite (36)

Picture
Malachite
Classification Carbonates
Chemical Composition Cu2(CO3)(OH)2
Hardness 3.5-4
Streak Light green
Luster Vitreous, silky, dull
Cleavage Basal
Fracture Irregular, uneven, subconchoidal
Density 3.6 - 4.05 g/cm3
Mineral Habit Botryoidal, massive, stalactitic
Crystal System Monoclinic
Environment of Formation In the oxidation zone of copper deposits
Economic Importance Pigment gemstone, minor copper ore


Native Elements

Copper (16)

Picture
Copper
Classification Native Element
Chemical Composition Cu
Hardness 2.5-3
Streak Shiny copper-red
Luster Metallic
Cleavage None
Fracture Hackly
Density 8.94 - 8.95 g/cm3
Mineral Habit Arborescent, nodular
Crystal System Isometric
Environment of Formation Most common in volcanic basalt rocks
Economic Importance Copper alloys, electricity, U.S. pennies

Diamond (18)

Picture
Diamond
Classification Native Element
Chemical Composition C
Hardness 10
Streak Colorless
Luster Adamantine
Cleavage Octahedral
Fracture Conchoidal
Density 3.5 - 3.53 g/cm3
Mineral Habit Euhedral, granular
Crystal System Isometric
Environment of Formation Formed with very high temperature and pressure in the mantle
Economic Importance Used in abrasives, small parts of mechanical devices, diamond windows (thin diamond membranes), jewelry

Gold (25)

Picture
Gold
Classification Native Element
Chemical Composition Au
Hardness 2.5-3
Streak Shiny yellow
Luster Metallic
Cleavage None
Fracture Hackly
Density 15 - 19.3 g/cm³
Mineral Habit Arborescent, granular, platy
Crystal System Isometric
Environment of Formation Trace amounts are found almost anywhere; there are only a few large deposits
Economic Importance Mostly jewelry, then coinage and a multitude of other uses, such as electronics, medicine, dentistry, computers, awards, pigments, gilding, and optics.

Graphite (26)

Picture
Graphite
Classification Native Element
Chemical Composition C
Hardness 1-2
Streak Metallic
Luster Black
Cleavage Basal
Fracture Conchoidal or sectile
Density 2.09 - 2.23 g/cm3
Mineral Habit Earthy, foliated, tabular
Crystal System Hexagonal
Environment of Formation High temperature and pressure in the upper mantle, also in metamorphic and igneous rocks
Economic Importance A wide range of uses in metallurgy and manufacturing, also commonly used in pencils

Silver (50)

Picture
Silver
Classification Native Element
Chemical Composition Ag
Hardness 2.5-3
Streak Silver-white
Luster Metallic
Cleavage None
Fracture Hackly
Density 10.1 - 11.1 g/cm3
Mineral Habit Arborescent, dendritic, massive
Crystal System Isometric
Environment of Formation In volcanic basalt rocks and in hydrothermal veins and mesothermal veins.
Economic Importance Used in jewelry, tableware, coins, electronics, photographic films, ornaments.

Sulfur (54)

Picture
Sulfur
Classification Native Element
Chemical Composition S
Hardness 1.5-2.5
Streak White
Luster Resinous
Cleavage Imperfect
Fracture Irregular, uneven, conchoidal
Density 2.07 g/cm³
Mineral Habit Massive, reniform, stalactitic
Crystal System Orthorhombic
Environment of Formation In sedimentary environments in evaporite and salt dome deposits, in volcanic deposits in hot springs and fumaroles, and in igneous basalt rocks of recent volcanic activity.
Economic Importance Mainly used to create sulfuric acid, also used for hydrogen sulfide, insecticides, herbicides, fungicides, pharmaceuticals, soaps, textiles, papers, processed rubber, gunpowder, leather, paint, dyes, food preservatives.

Halides

Fluorite (22)

Picture
Fluorite
Classification Halide
Chemical Composition CaF2
Hardness 4
Streak White
Luster Vitreous
Cleavage Perfect
Fracture Splintery, sub-conchoidal
Density 3.175 - 3.56 g/cm3
Mineral Habit Crystalline, disseminated, massive, granular
Crystal System Isometric
Environment of Formation Hydrothermal ore veins, sedimentary deposits, metamorphic environments, and pegmatite dikes.
Economic Importance Used in a wide variety of chemical, metallurgical, and ceramic processes.

Halite (30)

Picture
Halite
Classification Halide
Chemical Composition NaCl
Hardness 2.5
Streak White
Luster Vitreous
Cleavage Perfect
Fracture Conchoidal
Density 2.168 g/cm3
Mineral Habit Crystalline, euhedral, granular
Crystal System Isometric
Environment of Formation Evaporite deposits, sedimentary salt beds, and salt domes.
Economic Importance Crushed and used to control snow/ice, used as a nutrient, sed by the chemical industry.


Oxides/Hydroxides

Bauxite (8)

Picture
Bauxite
Classification Hydroxide
Chemical Composition AlO(OH)
Hardness 1-3
Streak White
Luster Dull
Cleavage None
Fracture Earthy
Density Approximately 3 g/cm3
Mineral Habit Massive, pisolitic
Crystal System Amorphous
Environment of Formation In the weathered surface zones in clay deposits and limestones, as well as low-silica igneous rocks
Economic Importance Aluminum ore, oilfield proppant

Corundum (17)

Picture
Corundum
Classification Oxide
Chemical Composition Al2O3
Hardness 9
Streak Colorless
Luster Vitreous, adamantine
Cleavage None (commonly exhibits rhombohedral and basal parting)
Fracture Irregular, uneven, conchoidal
Density 3.98 - 4.1 g/cm3
Mineral Habit Euhedral, prismatic, tabular
Crystal System Hexagonal
Environment of Formation In altered metamorphic rocks.
Economic Importance Used as an abrasive and commonly in jewelry.

Goethite/Limonite (21)

Picture
Goethite/Limonite
Classification Hydroxide/Oxide
Chemical Composition FeO(OH)·nH2O
Hardness 4-5.5
Streak Yellow to brown
Luster Silky, dull
Cleavage None
Fracture Irregular, uneven
Density 2.7 - 4.3 g/cm³
Mineral Habit Acicular, radial, reniform
Crystal System Orthorhombic
Environment of Formation Made from weathering of iron-bearing materials
Economic Importance Pigment and minor iron ore

Hematite (31)

Picture
Hematite
Classification Oxide
Chemical Composition Fe2O3
Hardness 5-6
Streak Red, reddish-brown
Luster Metallic, dull, earthy
Cleavage None (occasionally exhibits rhombohedral and basal parting)
Fracture Uneven
Density 5.26 g/cm³
Mineral Habit Tabular, earthy, blocky
Crystal System Trigonal
Environment of Formation Found in all rock types
Economic Importance Most important iron ore

Magnetite (45)

Picture
Magnetite
Classification Oxide
Chemical Composition Fe3O4
Hardness 5.5-6.5
Streak Black
Luster Metallic
Cleavage None
Fracture Subconchoidal, even
Density 5.175 g/cm³
Mineral Habit Crystalline, massive, granular
Crystal System Isometric
Environment of Formation Occurs in igneous and metamorphic rocks
Economic Importance Used as iron ore and to study the earth's magnetic field

Phosphates

Apatite (4)

Picture
Apatite
Classification Phosphate group
Chemical Composition Ca5(PO4)3(F,Cl,OH)
Hardness 5
Streak White
Luster Vitreous
Cleavage Indiscernible
Fracture Conchoidal
Density 3.1 - 3.2 g/cm3
Mineral Habit Earthy, colloform, massive, granular
Crystal System Hexagonal
Environment of Formation In every rock type
Economic Importance Fertilizer, phosphoric acid, hydrofluoric acid, gemstones, an ore of rare earth elements, pigments


Sulfates

Barite (9)

Picture
Barite
Classification Sulfate
Chemical Composition BaSO4
Hardness 3-3.5
Streak White
Luster Vitreous, pearly
Cleavage Basal, prismatic, pinacoidal
Fracture Irregular, uneven
Density 4.5 g/cm3
Mineral Habit Massive, prismatic, tabular
Crystal System Orthorhombic
Environment of Formation Often replaces other minerals in sedimentary rock layers and in hydrothermal and mesothermal metal ore veins
Economic Importance Drilling mud; high-density filler for paper, rubber, plastics

Celestite (14)

Picture
Celestite
Classification Sulfate
Chemical Composition SrSO4
Hardness 3-3.5
Streak White
Luster Vitreous, pearly
Cleavage Basal, prismatic, pinacoidal
Fracture Uneven
Density 3.96 - 3.98 g/cm3
Mineral Habit Crystalline, granular, massive
Crystal System Orthorhombic
Environment of Formation In sedimentary rock
Economic Importance Strontium ore; popular among collectors


Gypsum Varieties

Alabaster (27)

Picture
Alabaster
Classification Sulfate (gypsum variety)
Chemical Composition CaSO4 · 2H2O
Hardness 2
Streak White
Luster Vitreous, pearly
Cleavage Perfect, distinct
Fracture Uneven
Density Approximately 2.3 g/cm3
Mineral Habit Massive
Crystal System Monoclinic
Environment of Formation Found in layered sedimentary deposits and as an evaporite
Economic Importance Used in plaster, drywall, and cement

Satin Spar (28)

Picture
Satin Spar
Classification Sulfate (Gypsum variety)
Chemical Composition CaSO4 · 2H2O
Hardness 2
Streak White
Luster Silky, pearly
Cleavage None
Fracture Granular
Density 2.312 - 2.322 g/cm3
Mineral Habit Fibrous
Crystal System Monoclinic
Environment of Formation Found in layered sedimentary deposits and as an evaporite
Economic Importance Used in plaster, drywall, and cement

Selenite (29)

Picture
Selenite
Classification Sulfate (gypsum variety)
Chemical Composition CaSO4 · 2H2O
Hardness 2
Streak White
Luster Vitreous, pearly
Cleavage None
Fracture Uneven
Density 2.312 - 2.322 g/cm3
Mineral Habit Fibrous
Crystal System Monoclinic
Environment of Formation Found in layered sedimentary deposits and as an evaporite
Economic Importance Used in plaster, drywall, and cement


Sulfides

Bornite (12)

Picture
Bornite
Classification Sulfide
Chemical Composition Cu5FeS4
Hardness 3
Streak Dark grey to black
Luster Metallic
Cleavage Indescribable
Fracture Conchoidal
Density 5.06 - 5.09 g/cm3
Mineral Habit Granular, massive, reniform
Crystal System Orthorhombic
Environment of Formation In copper ore veins and hydrothermal metamorphic rocks
Economic Importance Ore of copper

Chalcopyrite (15)

Picture
Chalcopyrite
Classification Sulfide
Chemical Composition CuFeS2
Hardness 3.5-4
Streak Black with a greenish tint
Luster Metallic
Cleavage Poor, indistinct/indiscernible
Fracture Uneven
Density 4.1-4.3 g/cm3
Mineral Habit Druse, euhedral, striated
Crystal System Tetragonal
Environment of Formation In the sulfide zones of copper deposits
Economic Importance Most important copper ore

Galena (23)

Picture
Galena
Classification Sulfide
Chemical Composition PbS
Hardness 2.5-3
Streak Steel grey
Luster Metallic
Cleavage Cubic
Fracture Subconchoidal
Density 7.58 g/cm3
Mineral Habit Euhedral, granular, massive
Crystal System Isometric
Environment of Formation In various igneous, metamorphic, and sedimentary deposits
Economic Importance Lead ore

Pyrite (40)

Picture
Pyrite
Classification Sulfide
Chemical Composition FeS2
Hardness 6-6.5
Streak Black with a slightly green tinge
Luster Metallic
Cleavage None
Fracture Conchoidal
Density 4.8-5 g/cm3
Mineral Habit Druse, stalactitic, striated
Crystal System Isometric
Environment of Formation Forms at high and low temperatures and small quantities in all rock types
Economic Importance Ore/indicator of gold

Sphalerite (52)

Picture
Sphalerite
Classification Sulfide
Chemical Composition ZnS
Hardness 3.5-4
Streak White, light brown
Luster Resinous
Cleavage All sides form a dodecahedron
Fracture Conchoidal
Density 3.9-4.1 g/cm3
Mineral Habit Colloform, euhedral, granular
Crystal System Isometric
Environment of Formation In sedimentary limestone deposits, hypothermal veins and mesothermal veins, and in hydrothermal replacement deposits.
Economic Importance Primary zinc ore, also used as a specimen


Silicates

Beryl (10)

Picture
Beryl
Classification Silicate
Chemical Composition Be3Al2Si6O18
Hardness 7.5-8
Streak Colorless
Luster Vitreous, waxy
Cleavage Basal
Fracture Uneven, conchoidal
Density 2.63 - 2.92 g/cm3
Mineral Habit Columnar, crystalline, prismatic
Crystal System Hexagonal
Environment of Formation Mainly occurs in granite, rhyolite, and pegmatite
Economic Importance Gemstones, a minor ore of beryllium

Epidote (20)

Picture
Epidote
Classification Silicate
Chemical Composition Ca2(Al2,Fe)(SiO4)(Si2O7)O(OH)
Hardness 6-7
Streak White to colorless
Luster Vitreous, pearly, resinous
Cleavage Perfect
Fracture Uneven
Density 3.3 - 3.6 g/cm3
Mineral Habit Fibrous, massive, prismatic
Crystal System Monoclinic
Environment of Formation Found in igneous and metamorphic rocks
Economic Importance Minor gemstone use

Kaolinite (33)

Picture
Kaolinite
Classification Silicate
Chemical Composition Al2Si2O5(OH)4
Hardness 2-2.5
Streak White
Luster Dull, earthy
Cleavage Perfect
Fracture Earthy
Density 2.65 g/cm3
Mineral Habit Earthy
Crystal System Monoclinic
Environment of Formation As an altering mineral in igneous, metamorphic, and sedimentary environments
Economic Importance Used in pottery, ceramics, paper production, and some medicines

Olivine (38)

Picture
Olivine
Classification Silicate
Chemical Composition (Mg,Fe)2SiO4
Hardness 6.5-7
Streak Colorless
Luster Vitreous
Cleavage Poor
Fracture Conchoidal
Density 3.2-3.4 g/cm3
Mineral Habit Massive, granular
Crystal System Orthorhombic
Environment of Formation Found in dark, igneous rocks
Economic Importance Gemstones, part of earth's mantle, a mineral of peridot

Sodalite (51)

Picture
Sodalite
Classification Silicate
Chemical Composition Na8(Al6Si6O24)Cl2
Hardness 5.5-6
Streak White
Luster Vitreous, greasy
Cleavage Poor
Fracture Uneven, conchoidal
Density 2.2-2.3
Mineral Habit Massive, disseminated, granular
Crystal System Isometric
Environment of Formation Mostly in igneous rocks that crystallized from sodium-rich magma
Economic Importance Semiprecious gemstone; cheaper alternative to lapis lazuli

Staurolite (53)

Picture
Staurolite
Classification Silicate
Chemical Composition (Fe,Mg,Zn,Li)2Al9Si4O22(OH)2
Hardness 7-7.5
Streak White
Luster Vitreous, dull
Cleavage Distinct
Fracture Uneven, subconchoidal
Density 3.7-3.8 g/cm3
Mineral Habit Tabular, twinning is common
Crystal System Monoclinic
Environment of Formation In metamorphosed schists, gneisses, and shales
Economic Importance Used in geologic field work to assess a rock's metamorphic history

Talc (55)

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Talc
Classification Silicate
Chemical Composition Mg3Si4O10(OH)2
Hardness 1
Streak White
Luster Greasy, waxy, pearly
Cleavage Perfect
Fracture Uneven
Density 2.7-2.8 g/cm3
Mineral Habit Foliated, massive, scaly
Crystal System Monoclinic
Environment of Formation In metamorphic rocks
Economic Importance Used in plastics, ceramics, cosmetics, paper, paint, roofing, and rubber

Topaz (56)

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Topaz
Classification Silicate
Chemical Composition Al2SiO4(F,OH)2
Hardness 8
Streak Colorless
Luster Vitreous
Cleavage Basal
Fracture Subconchoidal
Density 3.4-3.6 g/cm3
Mineral Habit Crystalline, massive, prismatic
Crystal System Orthorhombic
Environment of Formation Generally formed in granites, pegmatites, and rhyolites
Economic Importance Gemstone

Tourmaline Group (57)

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Tourmaline
Classification Silicate group
Chemical Composition (Ca,Na,K,)(Li,Mg,Fe+2,Fe+3,Mn+2,Al,Cr+3,V+3)3(Mg,Al,Fe+3,V+3,Cr+3)6((Si,Al,B)6O18)(BO3)3(OH,O)3(OH,F,O)
Hardness 7-7.5
Streak White to colorless
Luster Vitreous
Cleavage Indistinct
Fracture Irregular, uneven, conchoidal
Density 2.9-3.1 g/cm3
Mineral Habit Prismatic
Crystal System Hexagonal
Environment of Formation Formed in granites, pegmatites, rhyolites, and some metamorphic environments
Economic Importance Popular gemstone and specimen


Amphibole Group

Hornblende (32)

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Hornblende
Classification Silicate (Amphibole)
Chemical Composition (Ca,Na)2-3(Mg,Fe,Al)5(Si,Al)8O22(OH,F)2
Hardness 5-6
Streak Colorless
Luster Vitreous, submetallic, dull
Cleavage Prismatic
Fracture Uneven, splintery
Density 2.9-3.4 g/cm3
Mineral Habit Prismatic, tabular, platy
Crystal System Monoclinic
Environment of Formation Found in metamorphic and igneous environments
Economic Importance Constituent of granite

Tremolite (58)

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Tremolite
Classification Silicate (Amphibole)
Chemical Composition Ca2(Mg,Fe)5Si8O22(OH)2
Hardness 5-6
Streak Colorless
Luster Vitreous, silky
Cleavage Prismatic
Fracture Uneven, splintery
Density 2.9-3.2
Mineral Habit Columnar, massive, fibrous, granular
Crystal System Monoclinic
Environment of Formation Found in igneous and metamorphic environments
Economic Importance Used in asbestos


Feldspar - Plagioclase

Albite (1)

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Albite
Classification Silicate (Plagioclase Feldspar)
Chemical Composition NaAlSi3O8
Hardness 6-6.5
Streak White
Luster Vitreous, pearly
Cleavage Basal, prismatic, pinacoidal
Fracture Subconchoidal, uneven
Density 2.6-2.63
Mineral Habit Blocky, granular, striated
Crystal System Triclinic
Environment of Formation Most often found in granites and pegmatites
Economic Importance Used in the manufacture of ceramics

Feldspar - Potassium

Amazonite/Microcline (3)

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Amazonite
Classification Silicate (Potassium Feldspar)
Chemical Composition KAlSi3O8
Hardness 6
Streak White
Luster Vitreous
Cleavage Basal, prismatic, pinacoidal
Fracture Conchoidal, uneven
Density 2.56-2.58 g/cm3
Mineral Habit Blocky, crystalline, prismatic
Crystal System Triclinic
Environment of Formation Found in pegmatites, metamorphic rocks, hydrothermal veins, and sedimentary conglomerates
Economic Importance Used in glass, ceramics, and jewelry

Orthoclase/Microcline (21)

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Orthoclase
Classification Silicate (Potassium Feldspar)
Chemical Composition KAlSi3O8
Hardness 6
Streak White
Luster Vitreous, pearly
Cleavage Basal, prismatic, pinacoidal
Fracture Conchoidal, uneven
Density 2.6 g/cm3
Mineral Habit Blocky, massive, granular, prismatic
Crystal System Monoclinic
Environment of Formation Low-temperature metamorphic rocks, pegmatites, and conglomerates
Economic Importance Used for glass, ceramics, and gemstones


Garnet Group

Almandine (2)

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Almandine
Classification Silicate (Garnet)
Chemical Composition Fe3Al2Si3O12
Hardness 7.5-8.5
Streak Colorless
Luster Vitreous
Cleavage None (may exhibit parting)
Fracture Conchoidal, uneven
Density 4.3 g/cm3
Mineral Habit Granular, massive, lamellar
Crystal System Isometric
Environment of Formation In regional metamorphic mica schist, contact metamorphic hornfels, diorite and granite pegmatites, and alluvial deposits
Economic Importance Used as an abrasive and a gemstone


Mica Group

Biotite (11)

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Biotite
Classification Silicate (Mica)
Chemical Composition K(Mg,Fe2+3)(Al,Fe3+)Si3O10(OH,F)2
Hardness 2.5-3
Streak White
Luster Pearly
Cleavage Perfect
Fracture Uneven
Density 2.8 - 3.4 g/cm3
Mineral Habit Lamellar, micaceous, pseudo-hexagonal
Crystal System Monoclinic
Environment of Formation Formed in metamorphic and igneous rocks; the primary mineral of rare earth pegmatites
Economic Importance Used in paints, in rubber products, and to date igneous rocks

Lepidolite (34)

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Lepidolite
Classification Silicate (Mica)
Chemical Composition K(Li,Al)3(Si,Al)4O10(F,OH)2
Hardness 2.5-3
Streak White
Luster Pearly
Cleavage Perfect
Fracture Uneven
Density 2.8 - 2.9 g/cm3
Mineral Habit Micaceous, pseudo-hexagonal
Crystal System Monoclinic
Environment of Formation Formed in high-lithium granite pegmatites
Economic Importance Most important lithium-bearing mineral; a secondary source of it

Muscovite (37)

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Muscovite
Classification Silicate (Mica)
Chemical Composition KAl3Si3O10(OH)2
Hardness 2-2.5
Streak Colorless
Luster Pearly
Cleavage Perfect
Fracture Uneven
Density 2.7-3 g/cm3
Mineral Habit Micaceous, foliated, massive
Crystal System Monoclinic
Environment of Formation Mostly in granite pegmatites, contact metamorphic rocks, metamorphic schists, and hydrothermal veins
Economic Importance Used in paint, rubber, drilling mud, and roofing


Pyroxene Group

Augite (6)

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Augite
Classification Silicate (Pyroxene)
Chemical Composition (Ca,Na)(Mg,Fe,Al)(Al,Si)2O6
Hardness 5-6
Streak Light green to colorless
Luster Vitreous, dull
Cleavage Prismatic (may exhibit parting)
Fracture Uneven
Density 3.2-3.6
Mineral Habit Columnar, granular, massive
Crystal System Monoclinic
Environment of Formation Mainly in igneous environments
Economic Importance No commercial uses

Rhodonite (49)

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Rhodonite
Classification Silicate (Pyroxene)
Chemical Composition MnSiO3
Hardness 5.5-6
Streak Colorless
Luster Vitreous
Cleavage Perfect
Fracture Hackly, uneven
Density 3.4-3.7 g/cm3
Mineral Habit Massive, granular, tabular
Crystal System Triclinic
Environment of Formation Manganese-rich metamorphic environments and hydrothermal replacement deposits
Economic Importance Decorative uses, jewelry; minor manganese ore


Quartz Varieties

Agate/Onyx (41)

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Agate/Onyx
Classification Silicate (Quartz variety)
Chemical Composition SiO2
Hardness 7
Streak White
Luster Vitreous
Cleavage None
Fracture Conchoidal
Density 2.6 g/cm3
Mineral Habit Crystalline, druse
Crystal System Hexagonal
Environment of Formation Occurs in all mineral environments
Economic Importance Used in electronics, glass, abrasives, and sand

Amethyst (42)

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Amethyst
Classification Silicate (Quartz variety)
Chemical Composition SiO2
Hardness 7
Streak White
Luster Vitreous
Cleavage None
Fracture Conchoidal
Density 2.6 g/cm3
Mineral Habit Crystalline, druse
Crystal System Hexagonal
Environment of Formation Occurs in all mineral environments
Economic Importance Used in electronics, glass, abrasives, and sand

Chalcedony (43)

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Chalcedony
Classification Silicate (Quartz variety)
Chemical Composition SiO2
Hardness 7
Streak White
Luster Vitreous
Cleavage None
Fracture Conchoidal
Density 2.6 g/cm3
Mineral Habit Crystalline, druse
Crystal System Hexagonal
Environment of Formation Occurs in all mineral environments
Economic Importance Used in electronics, glass, abrasives, and sand

Citrine (44)

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Citrine
Classification Silicate (Quartz variety)
Chemical Composition SiO2
Hardness 7
Streak White
Luster Vitreous
Cleavage None
Fracture Conchoidal
Density 2.6 g/cm3
Mineral Habit Crystalline, druse
Crystal System Hexagonal
Environment of Formation Occurs in all mineral environments
Economic Importance Used in electronics, glass, abrasives, and sand

Crystal (45)

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Crystal Quartz
Classification Silicate (Quartz variety)
Chemical Composition SiO2
Hardness 7
Streak White
Luster Vitreous
Cleavage None
Fracture Conchoidal
Density 2.6 g/cm3
Mineral Habit Crystalline, druse
Crystal System Hexagonal
Environment of Formation Occurs in all mineral environments
Economic Importance Used in electronics, glass, abrasives, and sand

Jasper (46)

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Jasper
Classification Silicate (Quartz variety)
Chemical Composition SiO2
Hardness 7
Streak White
Luster Vitreous
Cleavage None
Fracture Conchoidal
Density 2.6 g/cm3
Mineral Habit Crystalline, druse
Crystal System Hexagonal
Environment of Formation Occurs in all mineral environments
Economic Importance Used in electronics, glass, abrasives, and sand

Milky Quartz (47)

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Milky Quartz
Classification Silicate (Quartz variety)
Chemical Composition SiO2
Hardness 7
Streak White
Luster Vitreous
Cleavage None
Fracture Conchoidal
Density 2.6 g/cm3
Mineral Habit Crystalline, druse
Crystal System Hexagonal
Environment of Formation Occurs in all mineral environments
Economic Importance Used in electronics, glass, abrasives, and sand

Opal (38)

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Opal
Classification Silicate (Quartz variety)
Chemical Composition SiO2*nH2O
Hardness 5.5-6.5
Streak White
Luster Vitreous
Cleavage None
Fracture Conchoidal
Density 2.09 g/cm3
Mineral Habit Crystalline, druse
Crystal System Amorphous
Environment of Formation Occurs in all mineral environments
Economic Importance Used in electronics, glass, abrasives, and sand

Rose Quartz (48)

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Rose Quartz
Classification Silicate (Quartz variety)
Chemical Composition SiO2
Hardness 7
Streak White
Luster Vitreous
Cleavage None
Fracture Conchoidal
Density 2.6 g/cm3
Mineral Habit Crystalline, druse
Crystal System Hexagonal
Environment of Formation Occurs in all mineral environments
Economic Importance Used in electronics, glass, abrasives, and sand

National List

Actinolite

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Actinolite
Classification Silicate (Amphibole)
Chemical Composition Ca2(Mg,Fe)5Si8O22(OH)2
Hardness 5.5-6
Streak Colorless
Luster Vitreous, silky
Cleavage Prismatic
Fracture Uneven, splintery
Density 2.9-3.5
Mineral Habit Fibrous, splintery
Crystal System Monoclinic
Environment of Formation Metamorphic & Igneous rocks, Serpentine deposits, hydrothermal replacement deposits
Economic Importance Gemstone, asbestos

Kyanite

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Kyanite
Classification Silicate
Chemical Composition Al2SiO5
Hardness Anisotropic- vertical: 4.5-5.5; horizontal: 6-7
Streak White to colorless
Luster Vitreous, pearly
Cleavage Perfect
Fracture Splintery
Density 3.5-3.7 g/cm3
Mineral Habit Columnar, fibrous
Crystal System Triclinic
Environment of Formation Found mainly in metamorphic rocks
Economic Importance Used in industries that require heat resistance, such as railroads

Labradorite

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Labradorite
Classification Silicate (Plagioclase Feldspar)
Chemical Composition (Na,Ca)(Al,Si)4O8
Hardness 6-6.5
Streak White
Luster Vitreous, pearly
Cleavage Basal, prismatic, pinacoidal
Fracture Conchoidal, uneven
Density 2.6-2.8 g/cm3
Mineral Habit Crystalline, granular, striated
Crystal System Triclinic
Environment of Formation Found in sedimentary deposits made from the weathering of igneous or metamorphic rocks that contain feldspar
Economic Importance Architectural stone, gemstone, cabochon

Pyrolusite

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Pyrolusite
Classification Oxide
Chemical Composition MnO2
Hardness 6-6.5
Streak Bluish-black to black
Luster Metallic, dull, earthy
Cleavage Perfect
Fracture Splintery, uneven
Density 4.4-5.3 g/cm3
Mineral Habit Dendritic, earthy, reniform
Crystal System Tetragonal
Environment of Formation Oxidation product of weathered manganese minerals, also forms from stagnant shallow bog and swamp deposits
Economic Importance Major manganese ore

Rhodochrosite

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Rhodochrosite
Classification Carbonate
Chemical Composition MnCO3
Hardness 3.5-4
Streak White
Luster Vitreous to pearly
Cleavage Rhombohedral
Fracture Conchoidal to even
Density 3.3-3.6
Mineral Habit Rhombohedral and Scalenohedral crystals
Crystal System Hexagonal
Environment of Formation Hydrothermal veins, igneous Pegmatites
Economic Importance Gemstone, ore of Manganese

Rutile

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Rutile
Classification Oxide
Chemical Composition TiO2
Hardness 6-6.5
Streak White to light brown
Luster Adamantine, submetallic
Cleavage Basal
Fracture Uneven
Density 4.2-4.3
Mineral Habit Prismatic, acicular
Crystal System Tetragonal
Environment of Formation Igneous, Metamorphic
Economic Importance Titanium ore, white pigment

Spodumene

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Spodumene
Classification Silicate (Pyroxene)
Chemical Composition LiAlSi2O6
Hardness 6.5-7
Streak White
Luster Vitreous, silky
Cleavage Prismatic
Fracture uneven, splintery
Density 3.1-3.2
Mineral Habit Prismatic
Crystal System Monoclinic
Environment of Formation Lithium Pegmatites
Economic Importance Lithium ore, gemstones

Stilbite

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Stilbite
Classification Silicate (Zeolite)
Chemical Composition (Na,Ca,K)4-9Al9Si27O72 · n(H2O)
Hardness 3.5-4
Streak Colorless
Luster Vitreous, pearly, dull
Cleavage Perfect
Fracture Uneven
Density 2.1-2.2
Mineral Habit Tabular, platy
Crystal System Monoclinic
Environment of Formation Igneous, Metamorphic
Economic Importance Chemical filters, ornament

Turquoise

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Turquoise
Classification Phosphate
Chemical Composition CuAl6(PO4)4(OH)8•4(H2O)
Hardness 5-6
Streak Bluish-greenish-white
Luster Waxy
Cleavage Perfect
Fracture Conchoidal
Density 2.6-2.8
Mineral Habit Concretionary, encrustations, massive
Crystal System Triclinic
Environment of Formation As an alteration mineral in hydrothermal replacement deposits, usually in arid copper-bearing regions; in sedimentary and metamorphic rocks
Economic Importance Mainly jewelry

Zircon

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Zircon
Classification Silicates
Chemical Composition ZrSiO4
Hardness 7.5
Streak Colorless
Luster Vitreous, adamantine
Cleavage Poor, indistinct
Fracture Conchoidal, uneven
Density 4.6-4.7 g/cm3
Mineral Habit Crystalline, prismatic, tabular
Crystal System Tetragonal
Environment of Formation Most often in igneous environments, usually in pegmatites; also in high-grade metamorphic rocks
Economic Importance Ore of zirconium metal, ore of zirconium dioxide, whitening agents, white pigment, gemstones, radiometric and radioactive dating