antimony , Semimetallic to metallic chemical element (see metal), chemical symbol Sb, atomic number 51. Of its various allotropes, the most common is a lustrous, bluish, brittle, flaky solid. In nature antimony occurs chiefly as the gray sulfide mineral stibnite, Sb2S3. Pure antimony metal has no important uses, but its alloys and compounds are extremely useful. Some antimony alloys have the rare quality of expanding on solidifying; these are used for castings and for type metal. Alloys with lead are used in car batteries, bullets, and cable sheaths. Antifriction alloys with tin and lead (babbitt metals) are used as components of machine bearings. Antimony compounds (valences 3, 4, and 5) are widely used as flame retardants in paints, plastics, rubber, and textiles; others are used as paint pigments.