Sainfeldite is a rare hydrated calcium arsenate mineral typically found as tabular crystals or crusts in hydrothermal veins. It is most recognized for its occurrence in the mining districts of Sainte-Marie-aux-Mines, where it forms in association with other arsenic-rich species.
Is this sainfeldite?
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 sainfeldite with a known reference. Sainfeldite sits at Mohs 4, 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: colorless, light pink.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: aggregates, radial, rosette.
Often confused with
Sainfeldite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside sainfeldite
Minerals reported to co-occur with sainfeldite. 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)₂·4H₂O
- Mohs hardness
- 4
- Density
- 3.04 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Aggregates, radial, rosette
- Cleavage
- Perfect on {010}
- 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 sainfeldite
Classic worldwide localities
- Gabe Gottes and Glückauf mines, Rauenthal, near Sainte-Marie-aux-Mines, Haut-Rhin, France
- Salsigne mine, 15 km north of Carcassone, Aude, France
- Duranus, Alpes Maritimes, France
- Jáchymov (Joachimsthal), Czech Republic
- Anton mine, Heubachtal, near Schiltach, and the Sophia mine, near Wittichen, Black Forest, Germany
- Bou Azzer, Morocco
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, ferrarisite in float, you are in the right ground. Typical habit: aggregates, radial, rosette. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify sainfeldite?+
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Is sainfeldite safe to handle?+
What rocks look like sainfeldite?+
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Find sainfeldite on the map
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