Much of the golden orpiment on this specimen from China is the change from realgar (red crystals) to the orangy orpiment. This piece is about ten inches (250 m — Photo: cobalt123 from Phoenix, Arizona, USA · CC BY-SA 2.0
Orpiment
Also known as: Auripigment.
The deep orange-yellow arsenic sulfide — a historic pigment ('king's yellow') of volcanic fumaroles and hot springs.
Intro adapted from Wikipedia (CC BY-SA).
Orpiment is an IMA-recognized mineral species in the sulfide class, with the chemical formula As₂S₃.
It crystallizes in the monoclinic crystal system (space group P2_1/n). It is a member of the Orpiment structural group.
Key properties: Mohs hardness 1.5–2; specific gravity 3.49; typically yellow or orange; Pale lemon-yellow streak; Resinous, pearly on cleavage surface luster; optically biaxial.
IMA symbol Orp, grandfathered status — known before the IMA’s founding.
Found in low-temperature hydrothermal veins, hot springs and fumaroles; also commonly as an alteration product of arsenic minerals, especially realgar.
It is found associated with Stibnite, realgar, arsenic, calcite, barite, gypsum.
The name comes from the Latin auripigmentum, golden paint, in allusion to the color.
Collections: Collector Favorites, Rare & Remarkable.