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. Edtollite leaves a light brown streak.
- 3Read the lusterHold the specimen under a strong light. Edtollite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: brown-black, black.
- 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 metallic on Edtollite and adamantine to resinous to dull on Andradite.
How to tell apart: Streak differs, so Edtollite leaves light brown, Grossularite Garnet leaves white; luster reads metallic on Edtollite and vitreous on Grossularite Garnet.
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
- Metallic
- Transparency
- Translucent
- Crystal system
- Triclinic
- Crystal habit
- Prismatic Crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Skarn
Where rockhounds find edtollite
Classic worldwide localities
- Kola Peninsula, Russia
- Srednyaya Padma, Russia
Field-hunting tip
Look in skarn country, the host setting where edtollite typically forms. If you start seeing diopside, calcite, magnetite in float, you are in the right ground. Field specimens usually show a prismatic crystals habit, so 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?+
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Find edtollite on the map
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