Ferrarisite is a rare secondary arsenate mineral typically occurring as fragile, acicular crystal sprays within hydrothermal vein environments. It is most commonly found in association with other arsenic-bearing minerals in historical silver-mining districts. Due to its toxicity and extreme rarity, it is primarily sought after by advanced collectors of rare mineral species.
Is this ferrarisite?
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 ferrarisite with a known reference. Ferrarisite 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. Ferrarisite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Ferrarisite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, pale pink.
- 5Look at form & habitCrystal system: triclinic. Typical habit: acicular crystals.
Often confused with
Ferrarisite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside ferrarisite
Minerals reported to co-occur with ferrarisite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₅(AsO₃OH)₂(AsO₄)₂·9H₂O
- Mohs hardness
- 2
- Density
- 2.8 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Acicular Crystals
- Cleavage
- Perfect On {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Veins
- Typical price
- $50-300 per specimen
Where rockhounds find ferrarisite
Classic worldwide localities
- Jáchymov, Czech Republic
- Bou-Azzer, Morocco
Field-hunting tip
Look in hydrothermal veins country — that is the host setting where ferrarisite typically forms. If you start seeing arsenolite, pharmacolite, calcite in float, you are in the right ground. Field specimens usually show a acicular crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find ferrarisite on the map
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