Stibnite

Stibnite, sometimes called antimonite, is a sulfide mineral, the mineral form of antimony trisulfide (Sb2S3). Wikipedia describes it as a soft, metallic grey crystalline solid and the most important source of the metalloid antimony. It is grey when fresh and can turn superficially black through oxidation in air. The article says stibnite is toxic upon ingestion, with symptoms similar to those of arsenic poisoning. It says stibnite was used from protodynastic ancient Egypt as a medication and a cosmetic, and that pastes of Sb2S3 powder in fat or other materials have been used since about 3000 BC as eye cosmetics, called kohl, to darken the brows and lashes or draw a line around the eye. This entry rests on that one article.