Ulexite is famous for its fiber-optic properties, which allow it to transmit images from one side of a cut piece to the other, earning it the nickname 'TV Rock'. It typically forms as soft, white, cotton-like masses in evaporite basins and is highly sensitive to humidity, often dehydrating and becoming opaque if not stored properly.
Is this ulexite?
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 ulexite with a known reference. Ulexite sits at Mohs 2.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Ulexite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Ulexite typically shows a silky luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: triclinic. Typical habit: fibrous, acicular, rounded nodules.
Often confused with
Ulexite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside ulexite
Minerals reported to co-occur with ulexite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaCaB₅O₆(OH)₆·5H₂O
- Mohs hardness
- 2.5
- Density
- 1.96 g/cm³
- Streak
- White
- Luster
- Silky
- Transparency
- Translucent
- Crystal system
- Triclinic
- Crystal habit
- Fibrous, Acicular, Rounded Nodules
- Cleavage
- Perfect in One Direction
- Fluorescence
- Bright Yellow Under SW UV
- Rarity
- Common
- Uses
- Collector, Scientific Research
- Host rock
- Evaporite Deposits in Arid Salt Pans
- Typical price
- $5-30 for small pieces, $50+ for large polished specimens
Where rockhounds find ulexite
3 mapped spotsClassic worldwide localities
- Boron, California, USA
- Tarapaca, Chile
- Sijilmasa, Morocco
- Argentina
Field-hunting tip
Look in evaporite deposits in arid salt pans country — that is the host setting where ulexite typically forms. If you start seeing borax, kernite, halite in float, you are in the right ground. Field specimens usually show a fibrous, acicular, rounded nodules habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Oklahoma, Nevada — start trip planning there.
Common questions
How do you identify ulexite?+
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Can I find ulexite in the United States?+
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Find ulexite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
