Edtollite is a rare potassium sodium copper arsenate that forms prismatic crystals. It is a sublimate on basaltic scoria at an active volcanic fumarole. It was first described from the Arsenatnaya fumarole, Tolbachik Volcano, Kamchatka, Russia.
Is this edtollite?
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 edtollite with a known reference. Edtollite sits at Mohs 7, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light brown.
- 3Read the lusterHold the specimen under a strong light. Luster: semi-metallic.
- 4Match the color rangeCompare against the expected color range: brown-black, black, brown internal reflections.
- 5Look at form & habitCrystal system: triclinic. Typical habit: prismatic crystals.
Often confused with
Edtollite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Edtollite leaves light brown, Andradite leaves white; luster reads semi-metallic on Edtollite and adamantine to resinous, dull on Andradite.
How to tell apart: Streak differs, so Edtollite leaves light brown, Grossular leaves white; luster reads semi-metallic on Edtollite and vitreous to resinous on Grossular.
Often found alongside edtollite
Minerals reported to co-occur with edtollite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₂NaCu₅Fe³⁺O₂(AsO₄)₄
- Mohs hardness
- 7
- Density
- 4.264 g/cm³
- Colors
- Streak
- Light brown
- Luster
- Semi-metallic
- Transparency
- Translucent to almost opaque
- Crystal system
- Triclinic
- Crystal habit
- Prismatic crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A sublimate on basaltic scoria at an active volcanic fumarole
Where rockhounds find edtollite
Classic worldwide localities
- Arsenatnaya fumarole, Second scoria cone, Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik Volcano, Kamchatka, Russia
Field-hunting tip
Where it forms: A sublimate on basaltic scoria at an active volcanic fumarole. If you start seeing hematite, dmisokolovite, johillerite in float, you are in the right ground. Typical habit: prismatic crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify edtollite?+
Where is edtollite found?+
Is edtollite safe to handle?+
What rocks look like edtollite?+
What minerals are found with edtollite?+
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Find edtollite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
