BISMUTHINITE, a somewhat rare mineral, consisting of bismuth trisulphide (Bi,S3). It crystallizes in the orthorhombic system and is isomorphous with stibnite (SbaSa), which it closely resembles in appearance. It forms loose interlacing aggregates of acicular crystals, or as masses with a foliated or fibrous struc ture. An important character is the perfect cleavage in one direc tion parallel to the length of the needles. The colour is lead-grey. The hardness is 2; specific gravity 6.4-6.5.