Johillerite is an exceptionally rare arsenate mineral known primarily from the fumaroles of the Tolbachik volcano in Russia. It typically appears as small, tabular, blue-violet crystals formed during high-temperature volcanic activity.
Is this johillerite?
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 johillerite with a known reference. Johillerite 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. Johillerite leaves a white to very pale violet streak.
- 3Read the lusterHold the specimen under a strong light. Johillerite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: blue-violet.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals.
Often confused with
Johillerite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Tilasite is the harder of the two (Mohs 5 vs. 3.5); streak differs, so Johillerite leaves white to very pale violet, Tilasite leaves white.
How to tell apart: Berzeliite is the harder of the two (Mohs 5 vs. 3.5); streak differs, so Johillerite leaves white to very pale violet, Berzeliite leaves white; luster reads vitreous on Johillerite and resinous on Berzeliite.
Often found alongside johillerite
Minerals reported to co-occur with johillerite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaCuMg₃(AsO₄)₃
- Mohs hardness
- 3.5
- Density
- 4.15 g/cm³
- Colors
- Streak
- White to Very Pale Violet
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular Crystals
- Cleavage
- Perfect On {010}; Good On {100} and {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Fumarolic Deposits
Where rockhounds find johillerite
Classic worldwide localities
- Tsumeb, Namibia
Field-hunting tip
Look in fumarolic deposits country, the host setting where johillerite typically forms. If you start seeing tenorite, hematite, paratacamite in float, you are in the right ground. Field specimens usually show a tabular crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find johillerite on the map
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