Hillesheimite is a rare member of the zeolite group, typically occurring as delicate, fibrous, or acicular radiating clusters in volcanic basalt cavities. It is primarily recognized by its specific association with other zeolite minerals in the Eifel region of Germany.
Is this hillesheimite?
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 hillesheimite with a known reference. Hillesheimite sits at Mohs 4-5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Hillesheimite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Hillesheimite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, pale yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: fibrous aggregates, radiating needles.
Often confused with
Hillesheimite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside hillesheimite
Minerals reported to co-occur with hillesheimite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Ca,K,Na)₄Al₄Si₁₀O₂₈·12H₂O
- Mohs hardness
- 4-5
- Density
- 2.16 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Fibrous Aggregates, Radiating Needles
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Volcanic Vesicles in Basalt
- Typical price
- $20-100 micro to thumbnail
Where rockhounds find hillesheimite
Classic worldwide localities
- Hillesheim, Eifel, Germany
- Mount Somma, Italy
Field-hunting tip
Look in volcanic vesicles in basalt country — that is the host setting where hillesheimite typically forms. If you start seeing chabazite, phillipsite, analcime in float, you are in the right ground. Field specimens usually show a fibrous aggregates, radiating needles habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find hillesheimite on the map
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