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 3.5-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Dervillite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Dervillite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: dark gray, 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: Dervillite is noticeably harder (Mohs 3.5-4 vs. 2-2.5); streak differs — Dervillite leaves black, Proustite leaves scarlet; luster reads metallic on Dervillite and adamantine on Proustite.
How to tell apart: Dervillite is noticeably harder (Mohs 3.5-4 vs. 2.5); streak differs — Dervillite leaves black, Pyrargyrite leaves red; luster reads metallic on Dervillite and metallic to adamantine on Pyrargyrite.
How to tell apart: Dervillite is noticeably harder (Mohs 3.5-4 vs. 2-2.5).
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
- 3.5-4
- Density
- 6.6 g/cm³
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Tabular Crystals, Massive, Granular
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Veins
- Typical price
- $50-300 per specimen
Where rockhounds find dervillite
Classic worldwide localities
- Chañarcillo, Chile
- Sainte-Marie-aux-Mines, France
- Jáchymov, Czech Republic
Field-hunting tip
Look in hydrothermal veins country — that is the host setting where dervillite typically forms. If you start seeing proustite, pyrargyrite, native silver in float, you are in the right ground. Field specimens usually show a tabular crystals, massive, granular habit, so 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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