Orpiment is a distinctively bright yellow arsenic sulfide mineral often found associated with realgar in hydrothermal veins. It typically forms massive, foliated, or powdery masses and is highly prized by collectors for its vivid color, though its softness and toxicity require careful handling.
Is this anorpiment?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch anorpiment with a known reference. Anorpiment sits at Mohs 1.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: resinous on crystal faces, pearly on cleavage surfaces.
- 4Match the color rangeCompare against the expected color range: greenish-yellow.
- 5Look at form & habitCrystal system: triclinic. Typical habit: massive, foliated, or powdery coatings.
Often confused with
Anorpiment vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Anorpiment leaves yellow, Realgar leaves red-orange to red.
How to tell apart: Streak differs, so Anorpiment leaves yellow, Sulfur leaves white.
How to tell apart: Greenockite is the harder of the two (Mohs 3-3.5 vs. 1.5); streak differs, so Anorpiment leaves yellow, Greenockite leaves yellow-orange to brick-red; luster reads resinous on crystal faces, pearly on cleavage surfaces on Anorpiment and adamantine to resinous on Greenockite.
Often found alongside anorpiment
Minerals reported to co-occur with anorpiment. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- As₂S₃
- Mohs hardness
- 1.5
- Density
- 3.33 g/cm³
- Colors
- Streak
- Yellow
- Luster
- Resinous on crystal faces, pearly on cleavage surfaces
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Massive, foliated, or powdery coatings
- Cleavage
- Perfect and easy on {001}
- Rarity
- Common
- Uses
- Collector, Pigment (historical), Industrial (arsenic source)
- Host rock
- A very low-temperature hydrothermal mineral
Where rockhounds find anorpiment
Classic worldwide localities
- Palomo mine, Castrovirreyna Province, Huancavelica Department, Peru
Field-hunting tip
Where it forms: A very low-temperature hydrothermal mineral. If you start seeing dufrénoysite, muscovite, orpiment in float, you are in the right ground. Typical habit: massive, foliated, or powdery coatings. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify anorpiment?+
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What rocks look like anorpiment?+
What minerals are found with anorpiment?+
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Find anorpiment on the map
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