Cave pearls are small, rounded, spherical or ovoid concretions of calcite that form in limestone caves through the deposition of calcium carbonate around a nucleus. They are typically found in shallow cave pools where dripping water keeps the pearls in constant motion, preventing them from cementing to the pool floor.
Is this cave pearls?
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 cave pearls with a known reference. Cave Pearls sits at Mohs 3, 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: dull.
- 4Match the color rangeCompare against the expected color range: white, cream, gray, brown.
- 5Look at form & habitCrystal system: trigonal. Typical habit: spherical or ovoid concretionary aggregates.
Often found alongside cave pearls
Minerals reported to co-occur with cave pearls. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaCO₃
- Mohs hardness
- 3
- Density
- 2.71 g/cm³
- Streak
- White
- Luster
- Dull
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Spherical or ovoid concretionary aggregates
- Cleavage
- Perfect rhombohedral
- Fluorescence
- Often exhibits white or yellow under UV
- Rarity
- Common
- Uses
- Collector, Educational
- Host rock
- limestone solution caves
Where rockhounds find cave pearls
Classic worldwide localities
- Carlsbad Caverns, USA
- Lechuguilla Cave, USA
- Postojna Cave, Slovenia
- Grutas de Cacahuamilpa, Mexico
Field-hunting tip
Where it forms: limestone solution caves. If you start seeing calcite, aragonite in float, you are in the right ground. Typical habit: spherical or ovoid concretionary aggregates. Train your eye for that shape before scanning the outcrop.
More cave pearls photos
Common questions
How do you identify cave pearls?+
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Find cave pearls on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
