anorthoclase

from The Collaborative International Dictionary of English v.0.48

Anorthoclase \A*nor"tho*clase\, n. [Gr. 'an 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.
   [Webster 1913 Suppl.]