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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 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
- 2.63 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Acicular crystals
- Cleavage
- On {001}, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A post-mine low-temperature reaction product of carbonate gangue with arsenical solutions derived from arsenic (Sainte-Marie-aux-Mines, France)
Where rockhounds find ferrarisite
Classic worldwide localities
- Gabe-Gottes mine, Rauenthal, near Sainte-Marie-aux-Mines, Haut-Rhin, and at Duranus, Alpes-Maritimes, France
- Anton mine, Heubachtal, near Schiltach, Wittichen, Black Forest, in the Bauhaus district, Richelsdorf Mountains, Hesse, and at Ramsbeck, North Rhein-Westphalia, Germany
Field-hunting tip
Where it forms: A post-mine low-temperature reaction product of carbonate gangue with arsenical solutions derived from arsenic (Sainte-Marie-aux-Mines, France). If you start seeing picropharmacolite, pharmacolite, sainfeldite in float, you are in the right ground. Typical habit: acicular crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferrarisite?+
Where is ferrarisite found?+
Is ferrarisite safe to handle?+
What rocks look like ferrarisite?+
What minerals are found with ferrarisite?+
What kind of rock does ferrarisite form in?+
What is ferrarisite used for?+
Find ferrarisite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
