Amstallite is a rare calcium aluminum silicate mineral often found as delicate, colorless to white prismatic crystals. It primarily occurs in the amphibolites near Amstall, Austria, where it forms in fissures and cavities. Collectors prize it for its rarity and its distinct crystal morphology in radial clusters.
Is this amstallite?
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 amstallite with a known reference. Amstallite sits at Mohs 3-5, 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: monoclinic. Typical habit: acicular, prismatic.
Often confused with
Amstallite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside amstallite
Minerals reported to co-occur with amstallite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaAl(Si,Al)₄O₈(OH)₄·(H₂O,Cl)
- Mohs hardness
- 3-5
- Density
- 2.40 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular, prismatic
- Cleavage
- Good on {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In open fissures cutting pegmatitic schlieren, in hydrothermally altered graphite-bearing metamorphic rocks
Where rockhounds find amstallite
Classic worldwide localities
- Amstall graphite quarry, Amstall, Austria
Field-hunting tip
Where it forms: In open fissures cutting pegmatitic schlieren, in hydrothermally altered graphite-bearing metamorphic rocks. If you start seeing apatite, rutile, siderite in float, you are in the right ground. Typical habit: acicular, prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify amstallite?+
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What rocks look like amstallite?+
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Find amstallite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
