[moon-stohn] 
| 1. | Also called precious moonstone. a semitransparent or translucent, opalescent, pearly-blue variety of adularia, used as a gem. |
| 2. | any of several adularescent feldspars, as certain varieties of albite, labradorite, or oligoclase, used as gems. |
| 3. | (not used technically) any milky or girasol stone used as a gem. |
| moon·stone (mōōn'stōn') n. A variety of feldspar valued as a gem for its pearly translucence. |
moonstone
gem-quality feldspar mineral, a mixed sodium and potassium aluminosilicate, (K,Na)AlSi3O8, that shows a silvery or bluish iridescence. Nearly all commercial moonstones come from Dumbara District, Sri Lanka, where they occur in gem gravels and in acid granulites and pegmatites.
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