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 1.5, 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 to pearly.
- 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
- Ca₆(HAsO₄)₃(AsO₄)₂·10.5H₂O
- Mohs hardness
- 1.5
- Density
- 2.68-2.76 g/cm³
- Streak
- White
- Luster
- Vitreous to pearly
- Transparency
- Translucent to opaque
- Crystal system
- Monoclinic
- Crystal habit
- Acicular or fibrous radial aggregates
- Cleavage
- Perfect
- Fluorescence
- White under SW and LW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A recent weathering product in oxidizing arsenic-rich mineral deposits
Where rockhounds find guérinite
Classic worldwide localities
- Sterling Hill, Ogdensburg, Sussex Co., New Jersey, and in the Getchell mine, Potosi district, Humboldt Co., Nevada, USA
- Daniel mine, Schneeberg, Saxony, Germany
- Bauhaus district, Richelsdorf, Hesse, Germany
- Anton mine, Heubachtal, near Schiltach, and at Wittichen, Black Forest, Germany
- Sainte-Marie-aux-Mines, Haut-Rhin, France
Field-hunting tip
Where it forms: A recent weathering product in oxidizing arsenic-rich mineral deposits. If you start seeing realgar, erythrite, quartz in float, you are in the right ground. Typical habit: acicular or fibrous radial aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify guérinite?+
Where is guérinite found?+
Is guérinite safe to handle?+
What rocks look like guérinite?+
What minerals are found with guérinite?+
What kind of rock does guérinite form in?+
What is guérinite used for?+
Find guérinite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
