Colemanite is a significant borate mineral typically found in evaporite deposits in arid regions. It often forms beautiful, glassy, short-prismatic crystals or dense white masses and is highly prized by collectors for its strong white fluorescence under short-wave UV light.
Is this colemanite?
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 colemanite with a known reference. Colemanite sits at Mohs 4.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Colemanite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Colemanite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, gray, yellowish.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: short prismatic crystals, massive, granular, or radiated clusters.
Often confused with
Colemanite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Colemanite is noticeably harder (Mohs 4.5 vs. 2).
How to tell apart: Colemanite is noticeably harder (Mohs 4.5 vs. 3.5); luster reads vitreous on Colemanite and subvitreous on Howlite.
How to tell apart: Colemanite is noticeably harder (Mohs 4.5 vs. 2.5); luster reads vitreous on Colemanite and silky on Ulexite.
Often found alongside colemanite
Minerals reported to co-occur with colemanite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂B₆O₁₁·5H₂O
- Mohs hardness
- 4.5
- Density
- 2.42 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Short Prismatic Crystals, Massive, Granular, Or Radiated Clusters
- Cleavage
- Perfect in One Direction
- Fluorescence
- Often Bright White or Yellowish Under SW UV
- Rarity
- Uncommon
- Uses
- Industrial, Collector
- Host rock
- Evaporite Deposits in Arid Lake Beds
- Typical price
- $10-50 per specimen depending on size and crystal quality
Where rockhounds find colemanite
Classic worldwide localities
- Boron, California, USA
- Death Valley, California, USA
- Simav, Turkey
- Sijes, Argentina
Field-hunting tip
Look in evaporite deposits in arid lake beds country, the host setting where colemanite typically forms. If you start seeing borax, ulexite, kernite in float, you are in the right ground. Field specimens usually show a short prismatic crystals, massive, granular, or radiated clusters habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find colemanite on the map
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