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. ]
n. [ Ortho- + Gr. &unr_; to break. ] (Min.) Common or potash feldspar crystallizing in the monoclinic system and having two cleavages at right angles to each other. See Feldspar. [ 1913 Webster ]