orpiment

Orpiment is a yellow arsenic sulfide mineral with the chemical formula As2S3. It occurs as yellow to orange-yellow masses, sometimes with a greasy luster. It is relatively soft and brittle.

It forms in hydrothermal veins and low-temperature deposits, often alongside realgar (As4S4), cinnabar (HgS), and calcite. It is found in many mineral localities worldwide.

Historically, orpiment has been used as a pigment under the name orpiment. It provides a bright yellow color but is photolabile and slowly darkens with light exposure; it also decomposes on heating or grinding. Its arsenic content makes it highly toxic, so its use as pigment has declined and it is primarily of interest to mineral collectors and researchers.

In handling and storage, orpiment should be treated as a hazardous material. Avoid inhalation of dust and contact with skin; store in a sealed container away from heat and light. Hazardous waste disposal guidelines apply.

Orpiment is yellow; Realgar is orange-red; They are related arsenic sulfide minerals but differ in composition (As2S3 vs As4S4).