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, 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.
