Stibnite
Stibnite, also antimonite, massive, opaque mineral composed of antimony trisulfide and crystallizing in the orthorhombic system (see Crystal ). Stibnite is striated vertically with soft, black streaks, has a brilliant, metallic luster, and ranges from lead gray to black. It has a hardness of 2 and a specific gravity of 4.52 to 4.62. The crystals are often curved or bent during formation and become dull on continued exposure to light. Stibnite is important mainly as the principal ore of antimony . Known since prehistoric times, stibnite was used, in the powdered form, in the civilizations of ancient Egypt and Asia Minor to darken the eyebrows and make the eyes appear larger. Mined extensively throughout the world, it is often found in quartz veins in granite and gneiss, and may occur as a replacement in limestone and shale. It is also found in deposits of such minerals as galena, cinnabar, gold, and barite. The principal deposits of stibnite occur in Hunan Province of China.