Source : Webster's Revised Unabridged Dictionary (1913)

Anorthoclase \A*nor"tho*clase\, n. [Gr. ? priv. + orthoclase.]
   (Min.)
   A feldspar closely related to orthoclase, but triclinic. It
   is chiefly a silicate of sodium, potassium, and aluminium.
   Sp. gr., 2.57 -- 2.60.