Tolbachite is an extremely rare copper chloride mineral discovered in volcanic fumaroles. It is typically found as brown to golden brown, tabular crusts or small crystal coatings associated with other volcanic sublimates. Due to its solubility, it must be kept in a dry environment to prevent degradation.
Is this tolbachite?
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 tolbachite with a known reference. Tolbachite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellowish red.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly.
- 4Match the color rangeCompare against the expected color range: brown, golden brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: deliquescent, fibrous, mossy.
Often confused with
Tolbachite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Tolbachite leaves yellowish red, Eriochalcite leaves white; luster reads pearly on Tolbachite and vitreous on Eriochalcite.
How to tell apart: Atacamite is the harder of the two (Mohs 3-3.5 vs. 2); streak differs, so Tolbachite leaves yellowish red, Atacamite leaves apple-green; luster reads pearly on Tolbachite and adamantine to vitreous on Atacamite.
Often found alongside tolbachite
Minerals reported to co-occur with tolbachite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CuCl₂
- Mohs hardness
- 2
- Density
- 3.42 g/cm³
- Colors
- Streak
- Yellowish red
- Luster
- Pearly
- Transparency
- Semitransparent
- Crystal system
- Monoclinic
- Crystal habit
- Deliquescent, fibrous, mossy
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- As fumarolic incrustations on basalt (Tolbachik volcano, Russia); formed with other copper chlorides in an oxidized copper deposit (Bisbee, Arizona, USA)
Where rockhounds find tolbachite
Classic worldwide localities
- Southwest mine, Bisbee, Cochise Co., Arizona, USA
- Tolbachik fissure volcano, Kamchatka Peninsula, Russia
Field-hunting tip
Where it forms: As fumarolic incrustations on basalt (Tolbachik volcano, Russia); formed with other copper chlorides in an oxidized copper deposit (Bisbee, Arizona, USA). If you start seeing tenorite, euchlorine, dolerophanite in float, you are in the right ground. Typical habit: deliquescent, fibrous, mossy. Train your eye for that shape before scanning the outcrop.
Common questions
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Find tolbachite on the map
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