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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