Orpiment

Orpiment is the transparent yellow mineral arsenic sulfide (As₂S₃), formed as a hot-springs deposit or as a low-temperature product in hydrothermal veins. Its molecular weight is 246.04 and its composition is: arsenic 60.90% and sulfur 39.10%. The crystals belong to the monoclinic system.

It is often found in association with realgar. Finding places are: Copalnic, Romania; Andreas-Berg, Germany; Valais, Switzerland; and Çölemerik, Turkey.

The name is from the Latin, auripigmentum (golden pigment), in allusion to the vivid golden hue. Ancient Middle Eastern artists used orpiment, but Western artists did not use it until the 18th century, when production of artificial arsenic trisulfide was begun. Because of its extreme toxicity, it was abandoned, except for a very fine grade called king's yellow, which was used until cadmium yellow (CdS) became available in the early 19th century.

The mineral is used in the manufacturing of glass, especially infra-red transmitting glass. It is also used as a pigment in oil cloth and linoleum.