Searlesite is a rare borosilicate mineral typically found in evaporite deposits within ancient lake beds. Collectors should look for its characteristic bladed or radiating crystal clusters occurring within saline crusts.
Is this searlesite?
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 searlesite with a known reference. Searlesite 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, slightly pearly on cleavage surfaces.
- 4Match the color rangeCompare against the expected color range: white, light brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous, radial, spherical.
Often confused with
Searlesite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Colemanite is the harder of the two (Mohs 4.5 vs. 3.5).
How to tell apart: Luster reads vitreous, slightly pearly on cleavage surfaces on Searlesite and subvitreous, glimmering on Howlite.
How to tell apart: Searlesite is noticeably harder (Mohs 3.5 vs. 2.5).
Often found alongside searlesite
Minerals reported to co-occur with searlesite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaBSi₂O₅(OH)₂
- Mohs hardness
- 3.5
- Density
- 2.44-2.46 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous, slightly pearly on cleavage surfaces
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous, radial, spherical
- Cleavage
- Perfect on {100}; imperfect on {102}, {010}
- Fluorescence
- Blue green under SW UV; orange under LW UV
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Commonly interbedded with oil shales or marls (Green River Formation, USA); in boron-bearing evaporite deposits (California, USA); rarely in vugs in phonolite (Point of Rocks, New Mexico, USA)
Where rockhounds find searlesite
1 mapped spotsClassic worldwide localities
- Searles Lake, San Bernardino Co., in the Kramer borate deposit, Kern Co., and at Lake Tecopa, Inyo Co., California, USA
- Cave Springs Wash, Silver Peak Range, Esmeralda Co., Nevada, USA
- Point of Rocks, Colfax Co., New Mexico, USA
- Mont Saint-Hilaire, Quebec, Canada
- Kremna, near Tito Uzice
- Bela Stena, Yugoslavia
Field-hunting tip
Where it forms: Commonly interbedded with oil shales or marls (Green River Formation, USA); in boron-bearing evaporite deposits (California, USA); rarely in vugs in phonolite (Point of Rocks, New Mexico, USA). If you start seeing shortite, trona, pyrite in float, you are in the right ground. Typical habit: fibrous, radial, spherical. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in New Mexico. Start trip planning there.
Common questions
How do you identify searlesite?+
Where is searlesite found?+
Can I find searlesite in the United States?+
What rocks look like searlesite?+
What minerals are found with searlesite?+
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Find searlesite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
