spinel

spinel, magnesium aluminum oxide, MgAl 2O 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.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.

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The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.