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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: earthy.
- 4Match the color rangeCompare against the expected color range: white, greenish blue, gray, yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular, lath.
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); streak differs, so Kaatialaite leaves white, Scorodite leaves greenish white; luster reads earthy on Kaatialaite and vitreous to subadamantine, subresinous on Scorodite.
How to tell apart: Streak differs, so Kaatialaite leaves white, Pharmacosiderite leaves yellowish green; luster reads earthy on Kaatialaite and adamantine to greasy 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
- 2.64 g/cm³
- Streak
- White
- Luster
- Earthy
- Transparency
- Semitransparent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular, lath
- Cleavage
- Perfect in one direction
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral in a granite pegmatite (Kaatiala pegmatite, Finland); in an oxidized Ag–As vein in gabbro (Niederbeerbach, Germany)
Where rockhounds find kaatialaite
Classic worldwide localities
- U.S. mine, Gold Hill, Tooele Co., Utah, USA
- Kaatiala pegmatite, near Kuortane, Finland
- Glasberg, Niederbeerbach, Odenwald, Hesse, Germany
- Wittichen, Black Forest, Germany
- St. Andreasberg, Harz Mountains, Germany
- Lauta, near Marienberg, Saxony, Germany
Field-hunting tip
Where it forms: A secondary mineral in a granite pegmatite (Kaatiala pegmatite, Finland); in an oxidized Ag–As vein in gabbro (Niederbeerbach, Germany). If you start seeing arsenolite, löllingite, calcite in float, you are in the right ground. Typical habit: acicular, lath. 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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