What is Orpiment?
Orpiment is a vivid yellow arsenic sulfide with pearly flakes and blades, one of the most visually striking minerals of low-temperature hydrothermal veins.
Mineralogy and crystal structure
Reference formula: As2S3. Orpiment forms layered monoclinic structures and is the dimorph of anorpiment. Its bright colour is diagnostic in context, but the arsenic content means that a display specimen must be handled responsibly. Orpiment is classified with sulfides and has a monoclinic crystal system. Typical hardness is 1.5–2 on the Mohs scale and specific gravity is approximately 3.4–3.5.
Colour, lustre and habit
Typical colours include lemon-yellow, orange-yellow, golden, brown. The usual bladed, foliated, massive habit and pearly, resinous lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Orpiment forms in or is associated with low-temperature hydrothermal veins, volcanic fumaroles and oxidised arsenic-rich ore systems. Important documented localities include Peru, Romania, Turkey, China, Japan, Nevada and the former mines of Central Asia.
Golden colour with a serious chemistry
Orpiment is a perfect reminder that beauty and hazard can share one crystal. Its golden blades are a classic hydrothermal mineral, but arsenic makes preservation and handling part of the story.
Collecting and care
Do not grind, heat or use in jewellery; keep sealed, dry and away from children, food and pets, and avoid dust.
