Orpiment

Orpiment is a mineral. Its chemical formula is As₂S₃. It is an orange to yellow mineral. It has a Mohs hardness of 1.5 to 2 and a specific gravity of 3.46. It melts at 300°C and oxidizes to arsenic trioxide at higher temperatures. It is toxic because it gets a layer of arsenic trioxide on it by oxidation in the air.

Orpiment was used as a pigment because it was one of the only yellow pigments that they could find. It is used to remove hair from hides.

Orpiment was once used in artworks, medicine, and other applications. However, because of its toxicity and instability, it is not popular anymore.