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spinel

From: The Columbia Encyclopedia, Sixth Edition | Date: 2008

spinel magnesium aluminum oxide, MgAl ₂ O ₄ , a mineral crystallizing in the isometric system, usually as octahedrons. It occurs as an accessory mineral in basic igneous rocks, in aluminum-rich metamorphic rocks, and in contact-metamorphosed limestones. Common spinel usually ranges in color from dark green to brown or black, but transparent red, blue, and green varieties are found and are used as gemstones; Myanmar and Sri Lanka are the principal producing countries. Much gem-quality spinel is now produced synthetically.

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The Columbia Encyclopedia, Sixth Edition. Copyright 2008 Columbia University Press

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