Dervillite is a very rare silver arsenic sulfide mineral that typically occurs in silver-bearing hydrothermal deposits. It is best identified by its dark metallic luster and association with other silver sulfosalts in silver mining districts.
Is this dervillite?
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 dervillite with a known reference. Dervillite sits at Mohs 1-1.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: brownish black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, massive, granular.
Often confused with
Dervillite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Dervillite leaves black, Proustite leaves vermilion; luster reads metallic on Dervillite and adamantine on Proustite.
How to tell apart: Pyrargyrite is the harder of the two (Mohs 2.5 vs. 1-1.5); streak differs, so Dervillite leaves black, Pyrargyrite leaves purplish red; luster reads metallic on Dervillite and adamantine on Pyrargyrite.
How to tell apart: Streak differs, so Dervillite leaves black, Stephanite leaves iron-black.
Often found alongside dervillite
Minerals reported to co-occur with dervillite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ag₂AsS₂
- Mohs hardness
- 1-1.5
- Density
- 5.62 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals, massive, granular
- Cleavage
- Good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a Co–Ni–Fe–As deposit
Where rockhounds find dervillite
Classic worldwide localities
- Found on a museum specimen from the Gabe-Gottes mine, Sainte-Marie-aux-Mies, Haut-Rhin, France (type locality)
Field-hunting tip
Where it forms: In a Co–Ni–Fe–As deposit. If you start seeing arsenic, rammelsbergite, safflorite in float, you are in the right ground. Typical habit: tabular crystals, massive, granular. Train your eye for that shape before scanning the outcrop.
Common questions
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Find dervillite on the map
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