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Corundum Corundum is a crystalline form of aluminium oxide (Al2O3) with traces of iron, titanium and chromium. It is a rock-forming mineral. It is one of the naturally clear transparent materials, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red and padparadscha if a pink-orange, while all other colors are called sapphire. The name "corundum" is derived from the Tamil word "kuruntam" meaning "ruby." Because of corundum's hardness (pure corundum is defined to have 9.0 Mohs), it can scratch almost every other mineral. Corundum occurs as a mineral in mica schist, gneiss, and some marbles in Metamorphic terranes. It also occurs in low silica igneous syenite and nepheline syenite intrusives. It commonly occurs as a detrital mineral in stream and beach sands because of its hardness and resistance to weathering. (source: Wikipedia) Photos by Kelly's Rocks (www.kellysrocks.com - from whom I bought this sample) Return to List Back to Michael's Hobbies page Back to Michael Marcotte's HomePage