Cahnite is a rare borate mineral known primarily from the unique zinc ore deposits of Franklin and Ogdensburg, New Jersey. It is highly prized by collectors for its sharp, transparent tetragonal crystals that often display a distinctive yellow-green fluorescence under shortwave ultraviolet light.
Is this cahnite?
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 cahnite with a known reference. Cahnite sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Cahnite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Cahnite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: sphenoidal crystals, often twinned appearing pseudo-orthorhombic.
Often confused with
Cahnite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside cahnite
Minerals reported to co-occur with cahnite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂B₂(AsO₄)(OH)₄
- Mohs hardness
- 3
- Density
- 3.15 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Tetragonal
- Crystal habit
- Sphenoidal Crystals, Often Twinned Appearing Pseudo-orthorhombic
- Cleavage
- Distinct On {111}
- Fluorescence
- Bright Yellow-green Under SW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Veins in Metamorphosed Zinc Ore Deposits
- Typical price
- $50-500 depending on specimen size and clarity
Where rockhounds find cahnite
Classic worldwide localities
- Franklin Mine, New Jersey, USA
- Sterling Hill Mine, New Jersey, USA
Field-hunting tip
Look in hydrothermal veins in metamorphosed zinc ore deposits country — that is the host setting where cahnite typically forms. If you start seeing willemite, hardystonite, gahnite in float, you are in the right ground. Field specimens usually show a sphenoidal crystals, often twinned appearing pseudo-orthorhombic habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find cahnite on the map
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