Tillmannsite is a very rare mercury-silver telluride mineral typically found as microscopic grains within hydrothermal ore deposits. It is best identified through laboratory analysis of metallic phases in polished sections, as it rarely forms distinct macroscopic crystals.
Is this tillmannsite?
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 tillmannsite with a known reference. Tillmannsite sits at Mohs 3.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brownish red.
- 3Read the lusterHold the specimen under a strong light. Luster: adamantine.
- 4Match the color rangeCompare against the expected color range: red, brownish red.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: aggregates, pseudo octohedral.
Often confused with
Tillmannsite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Tillmannsite leaves brownish red, Tetrahedrite leaves black to brown; luster reads adamantine on Tillmannsite and metallic, commonly splendent on Tetrahedrite.
How to tell apart: Streak differs, so Tillmannsite leaves brownish red, Goldfieldite leaves black; luster reads adamantine on Tillmannsite and metallic on Goldfieldite.
Often found alongside tillmannsite
Minerals reported to co-occur with tillmannsite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (HgAg₃)VO₄
- Mohs hardness
- 3.5
- Density
- 7.769 g/cm³
- Colors
- Streak
- Brownish red
- Luster
- Adamantine
- Transparency
- Translucent
- Crystal system
- Tetragonal
- Crystal habit
- Aggregates, pseudo octohedral
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Supergene product in the oxidized zone of a copper deposit hosted in dolomite, calcite, and aragonite
Where rockhounds find tillmannsite
Classic worldwide localities
- Roua copper deposit, Var Valley (the Daluis gorge), northwest Alpes-Maritimes department, France
Field-hunting tip
Where it forms: Supergene product in the oxidized zone of a copper deposit hosted in dolomite, calcite, and aragonite. If you start seeing pecoraite, vésigniéite, olivenite in float, you are in the right ground. Typical habit: aggregates, pseudo octohedral. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify tillmannsite?+
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Find tillmannsite on the map
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