Orpiment
Orpiment is a soft arsenic sulfide mineral famous for its brilliant lemon to golden-yellow color and resinous luster. It forms in low-temperature veins and hot spring deposits, commonly alongside red-orange realgar.
Orpiment properties at a glance
| Type | Sulfide Minerals |
|---|---|
| Chemical formula | As2S3 |
| Mohs hardness | 1.75 |
| Crystal system | monoclinic |
| Luster | resinous |
| Streak | Pale lemon yellow |
| Cleavage | Perfect on {010} |
| Fracture | Uneven |
| Specific gravity | 3.49 |
| Transparency | translucent |
| Common colors | Lemon yellow, Golden yellow, Orange-yellow, Brownish yellow |
| Rarity | uncommon |
Geology & background
Orpiment is an arsenic sulfide that forms in low-temperature hydrothermal veins, hot spring deposits, and volcanic fumaroles, often together with the related arsenic mineral realgar.
Orpiment was used as a yellow pigment in art and manuscripts for thousands of years and was also valued in early medicine and alchemy before its toxicity was fully understood.
How to identify Orpiment
- Look for a soft, bright lemon to golden-yellow mineral with a resinous to pearly luster.
- Orpiment is very soft at about 1.5 to 2 and has one perfect cleavage that yields flexible flakes.
- Its pale yellow streak and association with red-orange realgar are strong identifying clues.
Where Orpiment is found
Orpiment occurs in low-temperature veins, hot springs, and fumaroles worldwide, with notable specimen localities in the United States, Peru, Russia, China, Romania, and Greece.
How much is Orpiment worth?
| Entry-level specimen | $10 |
|---|---|
| Typical collector specimen | $60 |
| Premium specimen | $400+ |
Value depends on color intensity, crystal development, luster, locality, size, and stability of the specimen.
Common uses
- Historical yellow pigment
- Collector specimens
- Mineralogical study
- Historical use in tanning and arts
Interesting facts
- Orpiment was once an important yellow pigment known as King's yellow, despite being highly toxic.
- Its name comes from the Latin auripigmentum, meaning gold pigment, for its rich yellow color.
- Orpiment and realgar are closely associated arsenic sulfides that often occur together.
- Realgar can slowly transform toward orpiment-like material after long exposure to light.
Care & safety
Orpiment is very soft and brittle and can flake apart or slowly degrade with light exposure.
Contains arsenic. Orpiment is an arsenic sulfide and is toxic; wash hands after handling and never ingest or inhale dust.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a proper respirator.
