Webster's Revised Unabridged Dictionary · 1913

Anorthoclase

Anorthoclase , noun

[Greek 'an priv. + orthoclase.]

(Mineralogy) A feldspar closely related to orthoclase, but triclinic. It is chiefly a silicate of sodium, potassium, and aluminium. Sp. gr., 2.57 -- 2.60.