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Corundum Family:
Simple Oxides (Aluminum oxide) Al3O3 AKA: Emery, Ruby, Sapphire |
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System: Hexagonal; sometimes tapering prismatic; also pyramidal, tabular; often striated. Appearance: White, gray brown to black, deep red (ruby), blue (sapphire), black from a mixture of magnetite, hematite or spinel (emery); vitreous, adamantine; streak white. Physical Properties: Hardness: (9.0); Specific gravity: (3.9 - 4.1). Cleavage: None; often conspicuous parting in three directions. Fracture, uneven, conchoidal; transparent to translucent; fluorescent; brittle. Similar species: Feldspars. The fine striations on parting faces might lead to confusion with the plagioclase feldspars, but corundum may be recognized by its superior hardness and high gravity. Occurrence: Corundum forms in several distinctive environments. It occurs associated with albite and acmite in nepheline syenite pegmatites; with andalusite and cordierite in hornfels of contact metamorphic rocks; and with muscovite, almandine and oligoclase in gneiss and hornfels of metamorphic terrains. Gem quality ruby and sapphire have only been found in a few places in North America, Montana and North Carolina. Large deposits of emery have been found in New York. Miscellaneous: Blood-red corundum is called ruby and is the rarest and most valuable gemstone. All other gem-quality corundum is called sapphire, and may be pink, blue, green, violet gray, yellow or other colors. May be clear or contain bundles of tubelike inclusions, giving "star" or "cat's eye" effect in cut or polished stones. The name is from kuruntam, a Tamil word derived from Sanskrit kuruvinda, "ruby". Corundum is used as an abrasive. Conventional Wisdom: Corundum promotes insight to the unknown. It stimulates ambition and confidence. It also dispels harsh and irritating attitudes and emotions, and helps one to release anger in a positive manner. It can be used in the treatment of disorders of the eyes, to sooth and smooth the skin, and to bring peace to the body. Belongs to the Astrological Sign of Sagittarius. |