Orpiment (As₂S₃) is the bright lemon-yellow to golden arsenic sulfide companion of realgar. Its name comes from Latin “auripigmentum” — gold pigment — referencing its long historical use as a pigment in painting and manuscripts. It forms in low-temperature hydrothermal veins, hot springs, and as a sublimation product around volcanic fumaroles, often intergrown with realgar.
Key Facts
- Mohs hardness 1.5–2 — soft and flexible foliated cleavage flakes.
- Resinous luster on broken faces; pearly on cleavage planes.
- Forms perfect 010 cleavage producing thin foliated sheets.
- Light-sensitive: prolonged sunlight degrades color, similar to realgar.
- Always paired with realgar in collector specimens — true twin minerals of the arsenic family.
Notable Chinese Localities
Tengchong (Yunnan) produces orpiment as a fumarolic deposit. Shimen Realgar Mine (Hunan) supplied the world with golden orpiment specimens during peak production decades. Twin Creeks Mine (Nevada, USA) is the modern world standard.
Found at these Localities
- Shimen Realgar-Orpiment Mine (石门雄黄雌黄矿)
- Yunnan (云南)
- Hunan (湖南)
