Ahlfeldite is a rare nickel-cobalt selenite mineral typically found as small, pale green to apple-green tabular crystals or crusts in oxidized zones of hydrothermal ore deposits. It is highly sought after by mineral collectors specializing in rare secondary species, particularly from its type locality in Bolivia.
Is this ahlfeldite?
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 ahlfeldite with a known reference. Ahlfeldite sits at Mohs 2-2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light green.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: pink brown, apple green, red.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic.
Often confused with
Ahlfeldite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Ahlfeldite leaves light green, Cobaltomenite leaves dark pink.
How to tell apart: Streak differs, so Ahlfeldite leaves light green, Erythrite leaves pale red to pink; luster reads vitreous on Ahlfeldite and subadamantine, pearly on cleavages on Erythrite.
Often found alongside ahlfeldite
Minerals reported to co-occur with ahlfeldite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NiSeO₃·2H₂O
- Mohs hardness
- 2-2.5
- Density
- 3.37 g/cm³
- Colors
- Streak
- Light green
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic
- Cleavage
- On {110} and {103}, fair
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare alteration product of nickel-bearing selenides and sulfides
Where rockhounds find ahlfeldite
Classic worldwide localities
- Pacajake mine, Hiaco, 24 km east-northeast of Colquechaca, and the El Dragón mine, 30 km southwest of Cerro Rico de Potosí, Potosí, Bolivia
Field-hunting tip
Where it forms: A rare alteration product of nickel-bearing selenides and sulfides. If you start seeing penroseite, chalcomenite, olsacherite in float, you are in the right ground. Typical habit: prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ahlfeldite?+
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Is ahlfeldite safe to handle?+
What rocks look like ahlfeldite?+
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Find ahlfeldite on the map
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