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, 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
How do you identify pentahydroborite?+
Where is pentahydroborite found?+
How much is pentahydroborite worth?+
What rocks look like pentahydroborite?+
What minerals are found with pentahydroborite?+
What kind of rock does pentahydroborite form in?+
What is pentahydroborite used for?+
Find pentahydroborite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
