Hexahydroborite is a rare calcium borate mineral that typically forms as delicate, radial fibrous aggregates or thin crusts in evaporite deposits. Due to its solubility and structural instability, it is primarily sought after by advanced collectors of borate minerals and is rarely seen in general collections.
Is this hexahydroborite?
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 hexahydroborite with a known reference. Hexahydroborite 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.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic.
Often confused with
Hexahydroborite 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. ~2.5).
How to tell apart: Howlite is the harder of the two (Mohs 3.5 vs. ~2.5); luster reads vitreous on Hexahydroborite and subvitreous, glimmering on Howlite.
Often found alongside hexahydroborite
Minerals reported to co-occur with hexahydroborite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaB₂O₄·6H₂O
- Mohs hardness
- ~2.5
- Density
- 1.84-1.87 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare component of boron-enriched skarn deposits in metasomatized limestones
Where rockhounds find hexahydroborite
Classic worldwide localities
- Solongo boron deposit, Buryatia, Russia
- Sayak-IV boron deposit, northeast Balkhash region, Kazakhstan
- Fuka, near Bicchu, Okayama Prefecture, Japan
Field-hunting tip
Where it forms: A rare component of boron-enriched skarn deposits in metasomatized limestones. If you start seeing pentahydroborite, frolovite, kurchatovite in float, you are in the right ground. Typical habit: prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify hexahydroborite?+
Where is hexahydroborite found?+
What rocks look like hexahydroborite?+
What minerals are found with hexahydroborite?+
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Find hexahydroborite on the map
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