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3.6: Mineral Appendix- Common Minerals and their Properties

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    Common Minerals and their Properties

    Amphibole: Hardness value right around glass (~5.5-6); green to black, elongate, or rod-shaped crystals common; two cleavage directions not at 90°.

    Augite: Hardness value right around glass (~5.5-6); blocky green to black crystals common; two cleavage directions at 90°.

    Biotite: Dark colored mica mineral; sheet cleavage (1 direction); flexible.

    Calcite: Reacts with HCl; rhombohedral shape and cleavage.

    Corundum: hexagonal shape with flat ends; hardness of 9; many colors common, lab kits generally have dull, brown or purple varieties. If gem quality, red = ruby; blue = sapphire.

    Dolomite: Reacts with HCl only when powdered; rhombohedral shape and cleavage.

    Fluorite: Commonly cleaves in octahedral shapes. Hardness is less than glass, but greater than copper. Many colors are common.

    Galena: High heft; cube-shaped crystals common; silvery-blue color.

    Garnet: Typically dark red in color (although there are many varieties); may have hackly or uneven fracture; dodecahedron shape common.

    Graphite: Soft, greasy feel; will leave marks on paper.

    Gypsum: Soft, may be tabular or fibrous; transparent to opaque.

    Halite: Cubic crystals common; waxy feel; taste is distinct.

    Hematite: Brick-red streak; may be earthy or metallic in luster.

    Hornblende: Hardness value right around glass (~5.5-6); green to black, elongate, or rod-shaped crystals common; two cleavage directions not at 90°.

    Kaolinite: Soft, earthy, white; massive; sticks to tongue.

    Kyanite: Blue color; bladed crystals; two different hardness values, H = 5, parallel to blade; H = 7 across blade.

    Magnetite: Magnetic; metallic; harder than glass.

    Muscovite: Colorless mica; sheet cleavage; transparent, flexible sheets.

    Olivine: Green color; granular or sugary feeling masses.

    Plagioclase feldspar var. Labradorite: Iridescent, dark gray; striations on cleavage faces; harder than glass.

    Plagioclase feldspar var. Albite: White to grey; striations on cleavage faces; harder than glass.

    Potassium feldspar: Commonly beige to pink or reddish, however Amazonite is blue-green; exsolution lamellae on cleavage faces; harder than glass.

    Pyrite: Metallic, brassy gold, cubic shape common; green-black streak.

    Pyroxene: Hardness value right around glass (~5.5-6); blocky green to black crystals common; two cleavage directions at 90°.

    Quartz: Harder than glass; glassy look; crystal shape, hexagonal prismatic; many colors common.

    Serpentine: Green, white, grey masses or fibrous. *Composes serpentinite, California’s state rock!

    Sphalerite: Yellow to black submetallic, vitreous, or resinous crystals with 6 cleavage faces; can form dodecahedrons; smells like rotten eggs when scratched, powdered, or treated with acid. Softer than glass (H=3.5-4).

    Sulfur: Yellow color and streak; light heft; brittle.

    Talc: Soft, greasy feel; pearly or dull luster common.

    Topaz: Harder than glass (H=8); adamantine luster, crystal shape, hexagonal prismatic; many colors common.

    Tourmaline: Crystals are long, slender to thick prismatic and columnar with a triangular cross-section; crystal faces may be striated. Color is commonly brown to black in color (Schorl), however, the pink version, watermelon tourmaline, can be found near San Diego, CA!

    Mineral Identification

    Metallic and Submetallic Minerals

    Hardness Cleavage Streak Characteristic Properties Mineral Name

    Hard (H > 5.5)

    Scratches glass

    No cleavage or cleavage not visible Dark gray/black Brassy gold; cubic shape common; H 6-6.5 Pyrite
    Silvery dark gray to black; magnetic; H 6-6.5 Magnetite
    Hard or Soft Red to brown Steel gray to reddish silver; may be earthy or metallic in luster; H 5-6 Hematite

    Soft (H ≤ 5.5)

    Does not scratch glass

    Visible cleavage Dark gray/black Silvery-blue; high heft; cleaves into cubic crystals; H 2.5 Galena
    White to pale yellow Silvery yellow-brown, red or black; submetallic to resinous luster; 6 cleavage planes; smells like rotten eggs when scratched or powdered; H 3.5-4 Sphalerite
    No cleavage or cleavage not visible Dark gray/black Dark silvery gray to black; soft, greasy feel; will leave marks on paper; H 1-2 Graphite

    Dark to Medium-Colored Nonmetallic Minerals

    Hardness Cleavage Characteristic Properties Mineral Name

    Hard (H > 5.5)

    Scratches glass

    Visible cleavage Iridescent blue-gray (var. Labradorite); striations on cleavage faces; 2 cleavages at 90°; H 6 Plagioclase feldspar
    Commonly beige, tan, pink, orange, or blue-green; exsolution lamellae on cleavage faces; 2 good cleavages at 90°; H 6 Potassium feldspar
    Green to black; elongate or rod-shaped crystals common; 2 cleavages at about 124° and 56°; H 5.5-6 Hornblende (an amphibole)
    Blocky green to black crystals; dull to vitreous luster; 2 cleavages at nearly right angles; H 5.5-6 Augite (a pyroxene)
    No cleavage or cleavage not visible Many colors common; vitreous luster; hexagonal prisms; transparent or translucent; H 7 Quartz
    Many colors common; hexagonal shapes with flat ends; generally dull, brown or purple; gem quality may be red (ruby) or blue (sapphire); H 9 Corundum
    Brown to dark red in color; may have hackly or uneven fracture; dodecahedron crystal form; H 7 Garnet
    Brown to black but other colors common in California; long slender to thick prismatic crystals; crystal faces may be striated; H 7-7.5 Tourmaline
    Olive green; granular or sugary feeling masses; no cleavage; vitreous luster; H 7 Olivine

    Soft (H ≤ 5.5)

    Does not scratch glass

    Visible cleavage Yellow-brown to black; vitreous to resinous luster; smells like rotten eggs when scratched or powdered; H 3.5-4 Sphalerite
    Purple cubes or octahedrons; H 4 Fluorite
    Dark colored mica; splits easily along 1 cleavage face into thin, flexible sheets; H 2.5-3 Biotite
    No cleavage or cleavage not visible Translucent or opaque dark green; soft, greasy feel; pearly or dull luster common; can easily be scratched with fingernail; H 1 Talc
    Red to red-brown; may be earthy or metallic in luster; characteristic brick-red streak; H 5-6 Hematite

    Light-Colored Nonmetallic Minerals

    Hardness Cleavage Characteristic Properties Mineral Name

    Hard (H > 5.5)

    Scratches glass

    Visible cleavage White to gray; striations on cleavage faces; 2 good cleavages at 90°; H 6 Plagioclase feldspar
    Commonly beige, tan, pink, orange, or blue-green; exsolution lamellae on cleavage faces; 2 good cleavages at 90°; H 6 Potassium feldspar
    Many colors common; adamantine luster; hexagonal prismatic shape; may display 1 perfect cleavage face; H 8 Topaz
    Blue; bladed crystals; H 5 parallel to blades; H 7 across blades Kyanite
    No cleavage or cleavage not visible Many colors common; hexagonal shapes with flat ends; generally dull, brown or purple; gem quality may be red (ruby) or blue (sapphire); H 9 Corundum
    Many colors common; vitreous luster; hexagonal prisms; transparent or translucent; H 7 Quartz
    Pale green to yellow color; granular or sugary feeling masses; no cleavage; vitreous luster; H 7 Olivine

    Soft (H ≤ 5.5)

    Does not scratch glass

    Visible cleavage Colorless, white, yellow, brown, green, pink; 3 excellent cleavages at 70°/110°; breaks into rhombohedrons; reacts with HCl; H 3 Calcite
    Colorless, white, gray, or pink; may display 3 excellent cleavages; effervesces only when powdered; H 3.5-4 Dolomite
    Transparent to opaque white or clear; may be tabular or fibrous; easily scratched with your fingernail; H 2 Gypsum
    Colorless to many colors; waxy feels; cubic crystals; salty taste; H 2.5 Halite
    Colorless, purple, blue, green, yellow; cleaves in octahedral shapes; H 4 Fluorite
    Colorless, yellow or brown mica; cleaves along 1 excellent cleavage into transparent, flexible sheets; H 2-2.5 Muscovite
    No cleavage or cleavage not visible Yellow; smells like rotten eggs when powdered; brittle; light heft; H 1.5-2.5 Sulfur
    Green, white, gray masses or fibrous; H 2.5-3.5 Serpentine
    Opaque white, gray, green, brown; soft, greasy feel; pearly or dull luster common; can easily be scratched with fingernail; H 1 Talc
    Soft, earthy, white; massive; sticks to tongue; powdery to greasy feel; H 1-2 Kaolinite

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