Dimorphite is a rare arsenic sulfide mineral found primarily in volcanic fumaroles as small, bright orange to yellow crystals. It is chemically unstable and tends to alter into realgar or other arsenic sulfides when exposed to light and air for extended periods.
Is this dimorphite?
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 dimorphite with a known reference. Dimorphite 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: adamantine.
- 4Match the color rangeCompare against the expected color range: orange.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular crystals, crusts, radial aggregates.
Often confused with
Dimorphite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Dimorphite leaves yellow, Realgar leaves red-orange to red; luster reads adamantine on Dimorphite and resinous to greasy on Realgar.
How to tell apart: Streak differs, so Dimorphite leaves yellow, Orpiment leaves pale lemon-yellow; luster reads adamantine on Dimorphite and resinous, pearly on cleavage surface on Orpiment.
Often found alongside dimorphite
Minerals reported to co-occur with dimorphite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- As₄S₃
- Mohs hardness
- 1.5
- Density
- 3.58 g/cm³
- Colors
- Streak
- Yellow
- Luster
- Adamantine
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular crystals, crusts, radial aggregates
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- Deposited at a fumerolic vent at temperatures of about 70°C–80°C (Solfatara, Italy); formed in an ore deposit under secondary conditions (Chile)
Where rockhounds find dimorphite
Classic worldwide localities
- Campania, from Solfatara di Pozzuoli, Campi Flegri, near Naples (type locality), and on Vesuvius, Italy
- Alacrán Ag–As–Sb mine, Pampa Larga district, Copiapó, Chile
Field-hunting tip
Where it forms: Deposited at a fumerolic vent at temperatures of about 70°C–80°C (Solfatara, Italy); formed in an ore deposit under secondary conditions (Chile). If you start seeing realgar, sal ammoniac, sulfur in float, you are in the right ground. Typical habit: tabular crystals, crusts, radial aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify dimorphite?+
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Find dimorphite on the map
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