moonstone

moonstone, an orthoclase feldspar, found in Sri Lanka, Myanmar, and Madagascar (and formerly in the St. Gotthard district of Switzerland). In spite of its pronounced cleavage, it is widely used as a gem. The refraction of light by its thin, paired internal layers causes its milky, bluish sheen.

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

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