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, 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
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Find proberite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
