Probertite is a hydrous sodium calcium borate mineral typically found in evaporite deposits of ancient dried-up lakes. It most commonly occurs as radiating sprays or tufts of acicular, needle-like crystals, which can be distinguished from the similar mineral ulexite by its slightly higher hardness and different crystal structure.
Is this proberite?
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 proberite with a known reference. Proberite 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. Proberite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Proberite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular crystals, radiating clusters, fibrous aggregates.
Often confused with
Proberite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside proberite
Minerals reported to co-occur with proberite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaCaB₅O₉·5H₂O
- Mohs hardness
- 3.5
- Density
- 2.13 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular Crystals, Radiating Clusters, Fibrous Aggregates
- Cleavage
- Perfect On {100}
- Rarity
- Uncommon
- Uses
- Collector, Scientific Research
- Host rock
- Evaporite Deposits in Lacustrine Basins
- Typical price
- $20-150 per specimen
Where rockhounds find proberite
2 mapped spotsClassic worldwide localities
- Boron, California, USA
- Tincalayu mine, Argentina
- Sijes, Argentina
Field-hunting tip
Look in evaporite deposits in lacustrine basins country — that is the host setting where proberite typically forms. If you start seeing borax, ulexite, colemanite in float, you are in the right ground. Field specimens usually show a acicular crystals, radiating clusters, fibrous aggregates habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Oklahoma — start trip planning there.
Common questions
How do you identify proberite?+
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Find proberite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
