Magnesiovoltaite is a rare sulfate mineral typically found as a secondary phase in the oxidized zones of ore deposits. It forms distinct, dark-colored cubic or cuboctahedral crystals that are structurally related to the voltaite group. Collectors usually identify it by its specific habit and association with other iron and magnesium sulfate minerals.
Is this magnesiovoltaite?
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 magnesiovoltaite with a known reference. Magnesiovoltaite sits at Mohs 2.5-3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Magnesiovoltaite leaves a greenish-yellow streak.
- 3Read the lusterHold the specimen under a strong light. Magnesiovoltaite typically shows a resinous luster.
- 4Match the color rangeCompare against the expected color range: black, dark green, dark brown.
- 5Look at form & habitCrystal system: cubic. Typical habit: cuboctahedral crystals.
Often confused with
Magnesiovoltaite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Magnesiovoltaite leaves greenish-yellow, Voltaite leaves greenish gray.
How to tell apart: Streak differs — Magnesiovoltaite leaves greenish-yellow, Copiapite leaves yellow; luster reads resinous on Magnesiovoltaite and pearly on Copiapite.
How to tell apart: Streak differs — Magnesiovoltaite leaves greenish-yellow, Jarosite leaves yellow; luster reads resinous on Magnesiovoltaite and vitreous on Jarosite.
Often found alongside magnesiovoltaite
Minerals reported to co-occur with magnesiovoltaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₂Mg₅Fe³⁺₃Al(SO₄)₁₂·18H₂O
- Mohs hardness
- 2.5-3
- Density
- 2.68 g/cm³
- Streak
- Greenish-yellow
- Luster
- Resinous
- Transparency
- Translucent
- Crystal system
- Cubic
- Crystal habit
- Cuboctahedral Crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Hydrothermal Sulfide Deposits
- Typical price
- $20-150 for small specimens
Where rockhounds find magnesiovoltaite
Classic worldwide localities
- Bajo de la Alumbrera, Argentina
- Cerro Quema, Panama
- United Verde Mine, Arizona, USA
- Chuquicamata Mine, Chile
Field-hunting tip
Look in oxidized zones of hydrothermal sulfide deposits country — that is the host setting where magnesiovoltaite typically forms. If you start seeing coquimbite, copiapite, jarosite in float, you are in the right ground. Field specimens usually show a cuboctahedral crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify magnesiovoltaite?+
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How much is magnesiovoltaite worth?+
What rocks look like magnesiovoltaite?+
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Find magnesiovoltaite on the map
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