Kottenheimite is a very rare hydrated calcium sulfate hydroxide mineral discovered in the volcanic fields of the Eifel region in Germany. It typically forms as delicate, white platy crystals or efflorescent crusts within cavities of volcanic rock. Due to its solubility and rarity, collectors should handle specimens with care and store them in stable, humidity-controlled conditions.
Is this kottenheimite?
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 kottenheimite with a known reference. Kottenheimite 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. Kottenheimite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Kottenheimite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: platy crystals, pseudohexagonal, efflorescent crusts.
Often confused with
Kottenheimite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside kottenheimite
Minerals reported to co-occur with kottenheimite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₄(SO₄)(OH)₆(H₂O)₁₂
- Mohs hardness
- 2
- Density
- 1.47 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Platy Crystals, Pseudohexagonal, Efflorescent Crusts
- Cleavage
- Perfect On {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Volcanic Ejecta, Specifically Leucite Tephrite
- Typical price
- $50-300 per specimen
Where rockhounds find kottenheimite
Classic worldwide localities
- Kottenheim, Eifel, Germany
- Mendig, Eifel, Germany
Field-hunting tip
Look in volcanic ejecta, specifically leucite tephrite country — that is the host setting where kottenheimite typically forms. If you start seeing ettringite, gypsum, thaumasite in float, you are in the right ground. Field specimens usually show a platy crystals, pseudohexagonal, efflorescent crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find kottenheimite on the map
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