mineral

Orpiment

Orpiment (As2S3)

Hardness: 1.5-2 on Mohs scale; Color: Lemon yellow to brownish-orange; Luster: Resinout to pearly; Crystal structure: Monoclinic; Cleavage: Perfect; Specific gravity: 3.49

Hardness: 1
Color: Lemon yellow to brownish-orange
Luster: Resinout to pearly

Identified May 3, 2026More mineral →

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Physical properties

Hardness: 1.5-2 on Mohs scale; Color: Lemon yellow to brownish-orange; Luster: Resinout to pearly; Crystal structure: Monoclinic; Cleavage: Perfect; Specific gravity: 3.49

Formation & geological history

Formed in low-temperature hydrothermal veins, volcanic fumaroles, and as an alteration product of other arsenic minerals like realgar. Common in sedimentary rocks as well.

Uses & applications

Historically used as a pigment (King's Yellow) and in alchemy; currently used in the manufacture of infrared-transmitting glass, semiconductors, and as a collector's specimen.

Geological facts

Orpiment was used by ancient painters but is highly toxic due to its arsenic content. It often occurs in association with the red mineral Realgar and can photosensitize, degrading over time if exposed to UV light.

Field identification & locations

Identify by its bright yellow-orange color and very soft, sectile texture. Found commonly in Nevada (USA), Peru, and China. Handle with gloves and wash hands after touching due to arsenic toxicity.