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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous; silky or satiny in fibrous aggregates.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: triclinic. Typical habit: acicular, capillary, fibrous.
Often confused with
Ulexite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads vitreous; silky or satiny in fibrous aggregates on Ulexite and subvitreous, pearly on {010} cleavages, silky if fibrous on Gypsum.
How to tell apart: Colemanite is the harder of the two (Mohs 4.5 vs. 2.5).
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
- 1.955 g/cm³
- Streak
- White
- Luster
- Vitreous; silky or satiny in fibrous aggregates
- Transparency
- Transparent to opaque
- Crystal system
- Triclinic
- Crystal habit
- Acicular, capillary, fibrous
- Cleavage
- On {010}, perfect; on {110}, good; on {110}, poor
- Fluorescence
- Weak yellow-white under SW and LW UV
- Rarity
- Common
- Uses
- Collector, Scientific research
- Host rock
- Typically in playa and salt-marsh deposits in arid regions and bedded sedimentary deposits formed from these, the boron supplied from surrounding hot springs
Where rockhounds find ulexite
3 mapped spotsClassic worldwide localities
- Columbus Marsh, Rhodes Marsh, and Teels Marsh, Esmeralda Co., Nevada, USA
- Death Valley and Saline Valley, Inyo Co., in the Kramer borate deposit, Boron, Kern Co., California, USA
- Iquique, and in a Surire salt lake, southeast of Arica, Tarapacá, Chile
- Salar de Ascotan, Antofagasta, Chile
- Jujuy, Salta, and Catamarca Provinces, Argentina
- Laguna Salinas, 70 km east of Arequipa, Peru
Field-hunting tip
Where it forms: Typically in playa and salt-marsh deposits in arid regions and bedded sedimentary deposits formed from these, the boron supplied from surrounding hot springs. If you start seeing colemanite, borax, meyerhofferite in float, you are in the right ground. Typical habit: acicular, capillary, fibrous. 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?+
What rocks look like ulexite?+
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Find ulexite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
