Hydroxylborite is a rare magnesium borate mineral typically found in metamorphic skarn environments. It usually appears as small, prismatic, colorless to yellowish crystals that are often closely associated with other borate species and calc-silicate minerals.
Is this hydroxylborite?
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 hydroxylborite with a known reference. Hydroxylborite sits at Mohs 4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Hydroxylborite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Hydroxylborite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic crystals, aggregates.
Often confused with
Hydroxylborite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Ludwigite is the harder of the two (Mohs 5 vs. 4); streak differs — Hydroxylborite leaves white, Ludwigite leaves black; luster reads vitreous on Hydroxylborite and submetallic on Ludwigite.
How to tell apart: Luster reads vitreous on Hydroxylborite and dull on Szaibelyite.
Often found alongside hydroxylborite
Minerals reported to co-occur with hydroxylborite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mg₃(BO₃)(OH,F,Cl)₃
- Mohs hardness
- 4
- Density
- 2.71 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic Crystals, Aggregates
- Cleavage
- Good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metamorphosed Limestone and Skarn Deposits
- Typical price
- $50-300 per specimen
Where rockhounds find hydroxylborite
Classic worldwide localities
- Långban, Sweden
- Kola Peninsula, Russia
Field-hunting tip
Look in metamorphosed limestone and skarn deposits country — that is the host setting where hydroxylborite typically forms. If you start seeing dolomite, calcite, tremolite in float, you are in the right ground. Field specimens usually show a prismatic crystals, aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find hydroxylborite on the map
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