Probertite is a borate mineral that typically forms distinct radial or divergent sprays of needle-like crystals. Collectors often value it for its excellent fluorescence under UV light and its tendency to occur in aesthetically pleasing spherical clusters within evaporite deposits.
Is this probertite?
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 probertite with a known reference. Probertite 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. Probertite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Probertite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: radial clusters, divergent fibrous aggregates, acicular crystals.
Often confused with
Probertite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside probertite
Minerals reported to co-occur with probertite. 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
- 2.14 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Radial Clusters, Divergent Fibrous Aggregates, Acicular Crystals
- Cleavage
- Perfect On {110}
- Fluorescence
- Bright White/cream Under SW and LW UV
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Evaporite Deposits in Saline Lake Beds
- Typical price
- $10-50 per specimen
Where rockhounds find probertite
Classic worldwide localities
- Boron, California, USA
- Salinas del Bebedero, Argentina
- Sultan Çayir, Turkey
Field-hunting tip
Look in evaporite deposits in saline lake beds country — that is the host setting where probertite typically forms. If you start seeing borax, ulexite, colemanite in float, you are in the right ground. Field specimens usually show a radial clusters, divergent fibrous aggregates, acicular crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify probertite?+
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Find probertite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
