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 — that is 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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