3.8: Mineral Appendix: Common Minerals and Their Properties

Mineral Appendix: Common Minerals and Their Properties

• Amphibole Links to an external site.: Hardness value right around glass (~5.5-6); green to black, elongate, or rod-shaped crystals common; two cleavage directions not at 90°.
• Augite Links to an external site.: Hardness value right around glass (~5.5-6); blocky green to black crystals common; two cleavage directions at 90°.
• Biotite Links to an external site.: Dark colored mica mineral; sheet cleavage (1 direction); flexible.
• Calcite Links to an external site.: Reacts with HCl; rhombohedral shape and cleavage.
• Corundum Links to an external site.: 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 Links to an external site.: Reacts with HCl only when powdered; rhombohedral shape and cleavage.
• Fluorite Links to an external site.: Commonly cleaves in octahedral shapes. Hardness is less than glass, but greater than copper. Many colors are common.
• Galena Links to an external site.: High heft; cube-shaped crystals common; silvery-blue color.
• Garnet Links to an external site.: Typically dark red in color (although there are many varieties); may have hackly Links to an external site. or uneven fracture; dodecahedron shape common.
• Graphite Links to an external site.: Soft, greasy feel; will leave marks on paper.
• Gypsum Links to an external site.: Soft, may be tabular or fibrous; transparent to opaque.
• Halite Links to an external site.: Cubic crystals common; waxy feel; taste is distinct.
• Hematite Links to an external site.: Brick-red streak; may be earthy or metallic in luster.
• Hornblende Links to an external site.: Hardness value right around glass (~5.5-6); green to black, elongate, or rod-shaped crystals common; two cleavage directions not at 90°.
• Kaolinite Links to an external site.: Soft, earthy, white; massive; sticks to tongue.
• Kyanite Links to an external site.: Blue color; bladed crystals; two different hardness values, H = 5, parallel to blade; H = 7 across blade.
• Magnetite Links to an external site.: Magnetic; metallic; harder than glass.
• Muscovite Links to an external site.: Colorless mica; sheet cleavage; transparent, flexible sheets.
• Olivine Links to an external site.: Green color; granular or sugary feeling masses.
• Plagioclase feldspar Links to an external site. var. Labradorite Links to an external site.: Iridescent, dark gray; striations on cleavage faces; harder than glass.
• Plagioclase feldspar Links to an external site. var. Albite Links to an external site.: White to grey; striations on cleavage faces; harder than glass.
• Potassium feldspar Links to an external site.: Commonly beige to pink or reddish, however Amazonite Links to an external site. is blue-green; exsolution lamellae on cleavage faces; harder than glass.
• Pyrite Links to an external site.: Metallic, brassy gold, cubic shape common; green-black streak.
• Pyroxene Links to an external site.: Hardness value right around glass (~5.5-6); blocky green to black crystals common; two cleavage directions at 90°.
• Quartz Links to an external site.: Harder than glass; glassy look; crystal shape, hexagonal prismatic; many colors common.
• Serpentine Links to an external site.: Green, white, grey masses or fibrous. *Composes serpentinite, California’s state rock!
• Sulfur Links to an external site.: Yellow color and streak; light heft; brittle.
• Talc Links to an external site.: Soft, greasy feel; pearly or dull luster common.
• Topaz Links to an external site.: Harder than glass (H=8); adamantine luster, crystal shape, hexagonal prismatic; many colors common.
• Tourmaline Links to an external site.: 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 Links to an external site., can be found near San Diego, CA!