3.6: Mineral Appendix- Common Minerals and their Properties

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Chloe Branciforte & Emily Haddad
Ventura College & East Los Angeles College via ASCCC Open Educational Resources Initiative

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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
Hard (H > 5.5) Scratches glass		Dark gray/black	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
	Visible cleavage	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
	No cleavage or cleavage not visible	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