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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous; pearly on cleavages.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: encrustations, fibrous.
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
- 2.85-2.96 g/cm³
- Streak
- White
- Luster
- Vitreous; pearly on cleavages
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Encrustations, fibrous
- Cleavage
- Perfect on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Formed by dehydration of pharmacolite (Getchell mine, Nevada, USA)
Where rockhounds find haidingerite
Classic worldwide localities
- White Caps mine, Manhattan district, Nye Co., and the Getchell mine, Potosi district, Humboldt Co., Nevada, USA
- Sterling Hill, Ogdensburg, Sussex Co., New Jersey, USA
- Jáchymov (Joachimsthal), Czech Republic
- Anton mine, Heubachtal, near Schiltach, and near Wittichen, Black Forest, Germany
- Richelsdorf, Hesse, Germany
- Gabe-Gottes mine, Rauenthal, near Sainte-Marie-aux-Mines, Haut-Rhin, France
Field-hunting tip
Where it forms: Formed by dehydration of pharmacolite (Getchell mine, Nevada, USA). If you start seeing pharmacolite, pitticite, weilite in float, you are in the right ground. Typical habit: encrustations, fibrous. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify haidingerite?+
Where is haidingerite found?+
Is haidingerite safe to handle?+
What rocks look like haidingerite?+
What minerals are found with haidingerite?+
What kind of rock does haidingerite form in?+
What is haidingerite used for?+
Find haidingerite on the map
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