ARGENTITE, a mineral consisting of silver sulphide It is occasionally found as uneven cubes and octahedra, but more often as dendritic or earthy masses, with a blackish lead-grey colour and metallic lustre. The mineral is perfectly sectile and has a shining streak; hardness 2.5, specific gravity '7.3. It occurs in mineral veins, and when found in large masses, as in Mexico and in the Comstock lode in Nevada, it is an important ore of silver. Silver sulphide is, however, cubic in crystallization only at temperatures above 91 ° C. ; the cubic crystals found in nature are really paramorphs, consisting of an intricate lamellar aggre gate of orthorhombic crystals. The orthorhombic modification of silver sulphide stable below 90 ° C. is the mineral acanthite.