Mineral Appendix: 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!
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!