Fabianite is a very rare borate mineral typically found in sedimentary evaporite sequences. It is best identified by its association with other borate species and its relatively high hardness for a borate mineral.
Is this fabianite?
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 fabianite with a known reference. Fabianite sits at Mohs 6, 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.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, massive.
Often confused with
Fabianite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside fabianite
Minerals reported to co-occur with fabianite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaB₃O₅(OH)
- Mohs hardness
- 6
- Density
- 2.77-2.796 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals, massive
- Cleavage
- On {110}
- Fluorescence
- Brownish yellow under SW and LW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a marine evaporite deposit
Where rockhounds find fabianite
Classic worldwide localities
- Drill core at Rehden, near Diepholz, Lower Saxony, Germany (type locality)
Field-hunting tip
Where it forms: In a marine evaporite deposit. If you start seeing halite, anhydrite, howlite in float, you are in the right ground. Typical habit: tabular crystals, massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify fabianite?+
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What rocks look like fabianite?+
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Find fabianite on the map
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