 Antimony is a chemical element with symbol Sb ( from Latin : stibium ) and atomic number 51 . A lustrous gray metalloid , it is found in nature mainly as the sulfide mineral stibnite ( Sb2S3 ) . Antimony compounds have been known since ancient times and were used for cosmetics ; metallic antimony was also known , but it was erroneously identified as lead upon its discovery . In the West , it was first isolated by <unk> Biringuccio and described in 1540 , although in primitive cultures its powder has been used to cure eye <unk> , as also for eye shadow , since time immemorial , and is often referred to by its Arabic name , kohl . 
