Pentahydroborite is a rare hydrated calcium borate mineral that typically forms delicate, needle-like acicular crystal clusters. It is most commonly found as white, glassy sprays coating the walls of cavities within borate-rich sedimentary deposits. Due to its scarcity and fragile nature, it is primarily sought after by advanced systematic mineral collectors.
Is this pentahydroborite?
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 pentahydroborite with a known reference. Pentahydroborite sits at Mohs 2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Pentahydroborite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Pentahydroborite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular or fibrous crystals, often as radiating sprays or crusts.
Often confused with
Pentahydroborite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Priceite is the harder of the two (Mohs 3-3.5 vs. 2); luster reads vitreous on Pentahydroborite and dull on Priceite.
How to tell apart: Howlite is the harder of the two (Mohs 3.5 vs. 2); luster reads vitreous on Pentahydroborite and subvitreous on Howlite.
Often found alongside pentahydroborite
Minerals reported to co-occur with pentahydroborite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaB₂O₄·5H₂O
- Mohs hardness
- 2
- Density
- 1.97 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular or Fibrous Crystals, Often as Radiating Sprays or Crusts
- Cleavage
- Perfect in One Direction
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Borate Deposits in Sedimentary Sequences
- Typical price
- $50-300 per specimen
Where rockhounds find pentahydroborite
Classic worldwide localities
- Nifegirskoe deposit, Sakha Republic, Russia
Field-hunting tip
Look in borate deposits in sedimentary sequences country — that is the host setting where pentahydroborite typically forms. If you start seeing colemanite, heidornite, gowerite in float, you are in the right ground. Field specimens usually show a acicular or fibrous crystals, often as radiating sprays or crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find pentahydroborite on the map
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