Phaunouxite is a rare calcium arsenate mineral that typically forms as delicate, white platy crystals or radial spray aggregates. It is found primarily in oxidized zones of arsenic-rich hydrothermal deposits and requires careful handling due to its arsenic content.
Is this phaunouxite?
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 phaunouxite with a known reference. Phaunouxite 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: colorless.
- 5Look at form & habitCrystal system: triclinic. Typical habit: platy crystals, radial aggregates.
Often confused with
Phaunouxite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside phaunouxite
Minerals reported to co-occur with phaunouxite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₃(AsO₄)₂·11H₂O
- Mohs hardness
- 2
- Density
- 2.28 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Triclinic
- Crystal habit
- Platy crystals, radial aggregates
- Cleavage
- On {100}, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A very rare post-mine low-temperature reaction product of carbonate gangue with arsenical solutions derived from arsenic (Sainte-Marie-aux-Mines, France)
Where rockhounds find phaunouxite
Classic worldwide localities
- Gabe-Gottes mine, Rauenthal, near Sainte-Marie-aux-Mines, Haut-Rhin, France
- Svatá Anna uranium deposit, Planá, near Mariánské Lázně (Marienbad), Czech Republic
- Schlema-Hartenstein, Saxony, and from the Bauhaus district, Richelsdorf Mountains, Hesse
- Muckross mine, Co. Kerry, Ireland
Field-hunting tip
Where it forms: A very rare 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: platy crystals, radial aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify phaunouxite?+
Where is phaunouxite found?+
Is phaunouxite safe to handle?+
What rocks look like phaunouxite?+
What minerals are found with phaunouxite?+
What kind of rock does phaunouxite form in?+
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Find phaunouxite on the map
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