Kaatialaite is a rare hydrated iron arsenate that typically forms as a secondary oxidation product of primary arsenic minerals in granite pegmatites. It is most often found as delicate, pearly-white to light gray platy crusts or radiating sprays of crystals. Due to its high arsenic content and relative scarcity, it is sought after primarily by systematic mineral collectors.
Is this kaatialaite?
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 kaatialaite with a known reference. Kaatialaite 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. Kaatialaite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Kaatialaite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: white, gray, greenish-white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: platy aggregates, crusts, or radiating bundles.
Often confused with
Kaatialaite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Scorodite is the harder of the two (Mohs 3.5-4 vs. 2); luster reads pearly on Kaatialaite and vitreous to sub-adamantine on Scorodite.
How to tell apart: Luster reads pearly on Kaatialaite and adamantine on Pharmacosiderite.
Often found alongside kaatialaite
Minerals reported to co-occur with kaatialaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe³⁺(AsO₃)₃·8H₂O
- Mohs hardness
- 2
- Density
- 3.5 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Platy Aggregates, Crusts, Or Radiating Bundles
- Cleavage
- Perfect in One Direction
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Granite Pegmatites
- Typical price
- $50-300 per specimen
Where rockhounds find kaatialaite
Classic worldwide localities
- Kaatiala, Finland
- Jáchymov, Czech Republic
Field-hunting tip
Look in granite pegmatites country — that is the host setting where kaatialaite typically forms. If you start seeing arsenopyrite, loellingite, quartz in float, you are in the right ground. Field specimens usually show a platy aggregates, crusts, or radiating bundles habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find kaatialaite on the map
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