Ammoniomagnesiovoltaite is a very rare sulfate mineral in the voltaite group, typically found as small, dark octahedral crystals. It forms primarily in the oxidized zones of mining environments where ammonium-rich solutions interact with magnesium and iron sulfides.
Is this ammoniomagnesiovoltaite?
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 ammoniomagnesiovoltaite with a known reference. Ammoniomagnesiovoltaite 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. Ammoniomagnesiovoltaite leaves a yellowish-green streak.
- 3Read the lusterHold the specimen under a strong light. Ammoniomagnesiovoltaite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: black, dark green, brown.
- 5Look at form & habitCrystal system: cubic. Typical habit: octahedral crystals, often with cube faces.
Often confused with
Ammoniomagnesiovoltaite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Ammoniomagnesiovoltaite leaves yellowish-green, Voltaite leaves greenish gray; luster reads vitreous on Ammoniomagnesiovoltaite and resinous on Voltaite.
How to tell apart: Streak differs — Ammoniomagnesiovoltaite leaves yellowish-green, Pickeringite leaves white; luster reads vitreous on Ammoniomagnesiovoltaite and silky on Pickeringite.
Often found alongside ammoniomagnesiovoltaite
Minerals reported to co-occur with ammoniomagnesiovoltaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (NH₄)₂Mg₅Fe³⁺₃Al(SO₄)₁₂·18H₂O
- Mohs hardness
- 2.5-3
- Density
- 2.14-2.18 g/cm³
- Colors
- Streak
- Yellowish-green
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Cubic
- Crystal habit
- Octahedral Crystals, Often with Cube Faces
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Sulfide-rich Ore Deposits, Coal Mine Dumps
- Typical price
- $20-150 for rare specimen fragments
Where rockhounds find ammoniomagnesiovoltaite
Classic worldwide localities
- United Verde Mine, Arizona, USA
- Coal mines, Czech Republic
- Various volcanic fumaroles
Field-hunting tip
Look in oxidized zones of sulfide-rich ore deposits, coal mine dumps country — that is the host setting where ammoniomagnesiovoltaite typically forms. If you start seeing gypsum, alunogen, jarosite in float, you are in the right ground. Field specimens usually show a octahedral crystals, often with cube faces habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ammoniomagnesiovoltaite?+
Where is ammoniomagnesiovoltaite found?+
How much is ammoniomagnesiovoltaite worth?+
What rocks look like ammoniomagnesiovoltaite?+
What minerals are found with ammoniomagnesiovoltaite?+
What kind of rock does ammoniomagnesiovoltaite form in?+
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Find ammoniomagnesiovoltaite on the map
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