Voltaite is a rare potassium-iron-aluminum sulfate mineral often forming in acidic mine environments or volcanic areas. It typically presents as dark, resinous octahedral crystals that may dehydrate and crumble if not stored in a humidity-controlled environment.
Is this voltaite?
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 voltaite with a known reference. Voltaite sits at Mohs 3-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Voltaite leaves a greenish gray streak.
- 3Read the lusterHold the specimen under a strong light. Voltaite typically shows a resinous luster.
- 4Match the color rangeCompare against the expected color range: black, greenish black.
- 5Look at form & habitCrystal system: cubic. Typical habit: octahedral crystals, often modified, massive or encrustations.
Often confused with
Voltaite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Voltaite is noticeably harder (Mohs 3-4 vs. 1.5-2); streak differs — Voltaite leaves greenish gray, Pickeringite leaves white; luster reads resinous on Voltaite and silky on Pickeringite.
How to tell apart: Voltaite is noticeably harder (Mohs 3-4 vs. 2); streak differs — Voltaite leaves greenish gray, Halotrichite leaves white; luster reads resinous on Voltaite and vitreous on Halotrichite.
How to tell apart: Streak differs — Voltaite leaves greenish gray, Copiapite leaves yellow; luster reads resinous on Voltaite and pearly on Copiapite.
Often found alongside voltaite
Minerals reported to co-occur with voltaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₂Fe²⁺₅Fe³⁺₃Al(SO₄)₁₂(OH)₂·18H₂O
- Mohs hardness
- 3-4
- Density
- 2.68 g/cm³
- Colors
- Streak
- Greenish Gray
- Luster
- Resinous
- Transparency
- Translucent
- Crystal system
- Cubic
- Crystal habit
- Octahedral Crystals, Often Modified, Massive or Encrustations
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Acid Mine Drainage Environments, Fumaroles, And Volcanic Sublimates
- Typical price
- $10-100 per specimen depending on crystal size and quality
Where rockhounds find voltaite
Classic worldwide localities
- Dalnegorsk, Russia
- Alum Cave Bluff, Tennessee, USA
- Chuquicamata, Chile
- Rammelsberg, Germany
Field-hunting tip
Look in acid mine drainage environments, fumaroles, and volcanic sublimates country — that is the host setting where voltaite typically forms. If you start seeing jarosite, melanterite, copiapite in float, you are in the right ground. Field specimens usually show a octahedral crystals, often modified, massive or encrustations habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find voltaite on the map
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