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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to silky.
- 4Match the color rangeCompare against the expected color range: colorless, violet, white.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: acicular, prismatic, stellate.
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)F₃
- Mohs hardness
- ~3.5
- Density
- 2.98 g/cm³
- Streak
- White
- Luster
- Vitreous to silky
- Transparency
- Translucent to transparent
- Crystal system
- Hexagonal
- Crystal habit
- Acicular, prismatic, stellate
- Cleavage
- On {0001}, good
- Fluorescence
- Yellow cream under SW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare hydrothermal mineral in skarns developed in metamorphosed boron-rich magnesian rocks
Where rockhounds find fluoborite
Classic worldwide localities
- Edenville and Amity, Orange Co., New York, USA
- Sterling Hill, Ogdensburg, in the Limecrest quarry, Sparta, and at the Edison quarry, Rudeville, Sussex Co., New Jersey, USA
- Blind Mountain, Bristol district, Lincoln Co., Nevada, USA
- Crestmore quarry, Riverside Co., California, USA
- Tallgruvan, east of Kallmora, Norberg, Sweden
- Cardiff mine and several roadcuts in the vicinity of Wilberforce, Ontario, Canada
Field-hunting tip
Where it forms: A rare hydrothermal mineral in skarns developed in metamorphosed boron-rich magnesian rocks. If you start seeing ludwigite, chondrodite, magnetite in float, you are in the right ground. Typical habit: acicular, prismatic, stellate. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify fluoborite?+
Where is fluoborite found?+
What rocks look like fluoborite?+
What minerals are found with fluoborite?+
What kind of rock does fluoborite form in?+
What is fluoborite used for?+
Find fluoborite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
