Haidingerite is a rare hydrous calcium arsenate typically found as delicate acicular crystals or radiating sprays in the oxidation zones of ore deposits. It is frequently associated with pharmacolite and serves as a secondary mineral resulting from the weathering of arsenic minerals. Collectors prize it for its fragile, white, needle-like formations which require careful handling.
Is this haidingerite?
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 haidingerite with a known reference. Haidingerite 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. Haidingerite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Haidingerite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular crystals, radiated sprays, crusts.
Often confused with
Haidingerite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside haidingerite
Minerals reported to co-occur with haidingerite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca(AsO₃OH)·H₂O
- Mohs hardness
- 2-2.5
- Density
- 2.28 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular Crystals, Radiated Sprays, Crusts
- Cleavage
- Perfect On {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Arsenic-rich Hydrothermal Deposits
- Typical price
- $50-300 per specimen
Where rockhounds find haidingerite
Classic worldwide localities
- Joachimsthal, Czech Republic
- Schneeberg, Germany
- Mapimi, Mexico
Field-hunting tip
Look in oxidized zones of arsenic-rich hydrothermal deposits country — that is the host setting where haidingerite typically forms. If you start seeing pharmacolite, arsenolite, picropharmacolite in float, you are in the right ground. Field specimens usually show a acicular crystals, radiated sprays, crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find haidingerite on the map
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