6o CHRYSOLITE FAMILY. nation ; and in other varieties two of the oppo site lateral planes disappear, when the planes that meet under acute angles form a 2. Four-sided prism. The crystals are generally blunt, or rounded on the angles and edges, even appear with convex lateral faces, and hence pass into longish grains. The crystals are generally middle-sized, seldom small, and occur either singly imbedded, as is the case with the grains, or in druses. Externally the crystals are sometimes smooth, some- '' times rough ; the first is shining and glistening, the other strongly glimmering. Internally it is shining, sometimes approaching to glis tening, and the lustre is vitreous, inclining to resinous. The principal fracture is foliated, generally rather im perfect, with a twofold slightly oblique cleavage; the cross fracture is uneven. The fragments are more or less sharp-edged. It occurs in distinct concretions, which are coarse or small, seldom fine, angulo-granular, and are so lopsely connected together, as frequently to be separable by the simple pressure of the fingers. Sometimes it occurs in longish granular concretions. The surfaces of the concretions are sometimes slightly rough and strongly glimmering, sometimes smooth and glistening. It is translucent, or translucent on the edges. It is hard in a low degree: it scratches glass. It is brittle. It is very easily frangible. Specific gravity, 3.316, D'Andrada. 3.303, Karstcn. 3.15, 3.06, Schumacher. 3.373, JIauy. Chemical
