||Ad`u*la"ri*a (&?;), n. [From Adula, a mountain peak in Switzerland, where fine specimens are found.] (Min.) A transparent or translucent variety of common feldspar, or orthoclase, which often shows pearly opalescent reflections; -- called by lapidaries moonstone.

• 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).