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, so 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, so Voltaite leaves greenish gray, Halotrichite leaves white; luster reads resinous on Voltaite and vitreous on Halotrichite.
How to tell apart: Streak differs, so 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, 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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