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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, may be satiny.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: radial.
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
- 2.135-2.141 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous, may be satiny
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Radial
- Cleavage
- On {110}, perfect
- Fluorescence
- Butter yellow to lemon yellow under SW and LW UV
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- In lake-bed deposits, the boron supplied by hydrothermal spring activity; may be an ore of boron
Where rockhounds find probertite
Classic worldwide localities
- Baker, Western Borax, and Suckow mines, Kramer borate deposit, Boron, Kern Co., California, USA
- Sterling borax mine, Lang, Los Angeles Co., California, USA
- Pacific Coast Borax Co. mine, Calico Hills, north of Daggett, San Bernardino Co., California, USA
- Southard, Blaine Co., Oklahoma, USA
- Tincalayu borax deposit, Salar del Hombre Muerto, Salta Province, Argentina
- One km south of Oficina Santa Luisa, Atacama, Chile
Field-hunting tip
Where it forms: In lake-bed deposits, the boron supplied by hydrothermal spring activity; may be an ore of boron. If you start seeing kernite, colemanite, ulexite in float, you are in the right ground. Typical habit: radial. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify probertite?+
Where is probertite found?+
What rocks look like probertite?+
What minerals are found with probertite?+
What kind of rock does probertite form in?+
What is probertite used for?+
Find probertite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
