Alumohydrocalcite is a rare hydrous calcium aluminum carbonate typically found as delicate, fibrous, or radiating spherical aggregates in alkalic igneous environments. Collectors prize it for its unique, delicate habit, though it is often small and requires magnification to appreciate its radial crystal structures.
Is this alumohydrocalcite?
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 alumohydrocalcite with a known reference. Alumohydrocalcite 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. Alumohydrocalcite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Alumohydrocalcite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, pale yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous, spherical, radiating clusters.
Often confused with
Alumohydrocalcite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Alumohydrocalcite is noticeably harder (Mohs 4 vs. 2).
How to tell apart: Alumohydrocalcite is noticeably harder (Mohs 4 vs. 3).
How to tell apart: Alumohydrocalcite is noticeably harder (Mohs 4 vs. 1-2); luster reads pearly on Alumohydrocalcite and dull on Huntite.
Often found alongside alumohydrocalcite
Minerals reported to co-occur with alumohydrocalcite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaAl₂(CO₃)₂(OH)₄·3H₂O
- Mohs hardness
- 4
- Density
- 2.23-2.27 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous, Spherical, Radiating Clusters
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Cavities in Alkalic Rocks and Carbonatites
- Typical price
- $20-100 for small clusters
Where rockhounds find alumohydrocalcite
Classic worldwide localities
- Kovdor, Russia
- Ashio, Japan
- Kropivnik, Czech Republic
Field-hunting tip
Look in hydrothermal cavities in alkalic rocks and carbonatites country — that is the host setting where alumohydrocalcite typically forms. If you start seeing calcite, dolomite, aragonite in float, you are in the right ground. Field specimens usually show a fibrous, spherical, radiating clusters habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify alumohydrocalcite?+
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What rocks look like alumohydrocalcite?+
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Find alumohydrocalcite on the map
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