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, so 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, so 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, 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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