from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A variety of transparent or translucent orthoclase.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A variety of orthoclase feldspar found as colorless to white prismatic crystals in cavities in metamorphic rocks. Some specimens reflect a bluish sheen along crystal faces. This phenomenon is called adularescence, and adularia with this property is called moonstone. (See sanidine).
from the GNU version of the Collaborative International Dictionary of English
- n. A transparent or translucent variety of common feldspar, or orthoclase, which often shows pearly opalescent reflections; -- called by lapidaries moonstone.
from The Century Dictionary and Cyclopedia
- n. A variety of the common potash feldspar orthoclase, occurring in highly lustrous transparent or translucent crystals. It often exhibits a delicate opalescent play of colors, and is then called moonstone (which see). Fine specimens are obtained from various localities in the Alps.
Italian, from French adulaire, after Adula, a mountain group of southeast Switzerland.(American Heritage® Dictionary of the English Language, Fourth Edition)