stibnite, antimony sulfide (Sb2S3), the principal ore of antimony. This mineral has a brilliant metallic lustre, is lead- to steel-gray in colour, and fuses readily in a candle flame (at about 525° C [977° F]). It often possesses a bladed habit, is striated, and has one perfect cleavage. Stibnite occurs in massive forms in gneiss and granite. It is also found in limestone, presumably deposited by hot springs. Significant deposits of stibnite have been located in Hunan province, China; on the island of Shikoku, Japan; and in the western United States (Idaho, California, and Nevada).
Stibnite and the analogous sulfides of arsenic and bismuth (orpiment and bismuthinite, respectively) form a group of minerals that have similar physical properties (see sulfide mineral [table]). Stibnite is used in the manufacture of matches, fireworks, and percussion caps and was used by the ancients as a cosmetic to increase the apparent size of the eye. Its crystals belong to the orthorhombic system.