TRAPEZOHEDRAL CLASS (Trapezohedral-hemihedral.) Six dyad axes of two kinds are perpen dicular to the hexad axis. The general form { hikl } is the hexagonal trapezohedron bounded by twelve trapezoidal faces. The other simple forms are geometrically the same as in the holosymmetric class. Quartz at temperatures above 5 7 C (and below 87o° C)—f3-quartz, bar ium-antimonyl dextro-tartrate +potassium nitrate and the corresponding lead salt crystallize in this class.