Guérinite is a rare hydrated calcium arsenate mineral that typically occurs as delicate, white, acicular crystal sprays or fibrous crusts. It is most frequently found in the oxidation zones of arsenic-rich hydrothermal vein deposits. Due to its fragility and toxic arsenic content, it is primarily a specimen for advanced mineral collectors.
Is this guérinite?
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 guérinite with a known reference. Guérinite sits at Mohs 2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Guérinite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Guérinite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular or fibrous radial aggregates.
Often confused with
Guérinite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside guérinite
Minerals reported to co-occur with guérinite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₅(AsO₄)₂(AsO₃OH)₂·9H₂O
- Mohs hardness
- 2
- Density
- 2.44 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular or Fibrous Radial Aggregates
- Cleavage
- Perfect On {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Veins in Arsenic-rich Ore Deposits
- Typical price
- $20-150 thumbnail specimens
Where rockhounds find guérinite
Classic worldwide localities
- Jáchymov, Czech Republic
- Schneeberg, Germany
- Wittichen, Germany
- Bou Azzer, Morocco
Field-hunting tip
Look in hydrothermal veins in arsenic-rich ore deposits country — that is the host setting where guérinite typically forms. If you start seeing pharmacolite, haidingerite, picropharmacolite in float, you are in the right ground. Field specimens usually show a acicular or fibrous radial aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find guérinite on the map
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