adularia

[In Ger. adular; Fr. & Ital. adulaire, from Mount Adula, in the Grisons in Switzerland, whence it is believed that the first specimens were brought.] One of the minerals called Moonstone. It is a subvariety of Orthoclase. Dana divides Orthoclase into two varieties: (1) Ordinary Orthoclase; (2) Compact Orthoclase, or orthoclase-felsite. Under the former of these he ranks thirteen sub-varieties, of which adularia is the first. It is transparent, is cleavable, and in most cases has opalescent reflections. Specific gravity, 2:539 to 2.578. It occurs on Snowdon, in the Isle of Arran, and at various places abroad.