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, 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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