Fluoborite is a rare magnesium borate mineral that typically forms in contact metamorphic zones within limestone. It is most frequently recognized by its hexagonal, prismatic crystal habit, often occurring in radiating clusters or fine-grained masses alongside other contact minerals like magnetite and calcite.
Is this fluoborite?
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 fluoborite with a known reference. Fluoborite sits at Mohs 3.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Fluoborite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Fluoborite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, yellow, violet.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: prismatic crystals, sometimes fibrous or massive.
Often confused with
Fluoborite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside fluoborite
Minerals reported to co-occur with fluoborite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mg₃(BO₃)(F,OH)₃
- Mohs hardness
- 3.5
- Density
- 2.9-3.0 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Hexagonal
- Crystal habit
- Prismatic Crystals, Sometimes Fibrous or Massive
- Cleavage
- Perfect On {0001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metamorphosed Limestones and Skarns
- Typical price
- $20-150 thumbnail
Where rockhounds find fluoborite
Classic worldwide localities
- Sweden
- USA
- Russia
- Italy
Field-hunting tip
Look in metamorphosed limestones and skarns country — that is the host setting where fluoborite typically forms. If you start seeing calcite, dolomite, magnetite in float, you are in the right ground. Field specimens usually show a prismatic crystals, sometimes fibrous or massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find fluoborite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
