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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 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
- Ca₂B(AsO₄)(OH)₄
- Mohs hardness
- ~3
- Density
- 3.156 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Tetragonal
- Crystal habit
- Sphenoidal crystals, often twinned appearing pseudo-orthorhombic
- Cleavage
- On {110}, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A late-stage mineral in pegmatites cutting a metamorphosed stratiform zinc orebody (Franklin, New Jersey, USA); with zeolites in leucitic lava (Capo di Bove, Italy)
Where rockhounds find cahnite
Classic worldwide localities
- Franklin, Sussex Co., New Jersey, USA
- Klodeborg mine, Arendal, Norway
- Capo di Bove, and Vallerano, Strada Laurentina, near Rome, Lazio, Italy
- Kombat Cu–Pb–Ag mine, 49 km south of Tsumeb, Namibia
- Killik, Hisarcık, and Espey borate mines, near Emet, Kütahya Province, Turkey
- Solongo boron deposit, Buryatia, Russia
Field-hunting tip
Where it forms: A late-stage mineral in pegmatites cutting a metamorphosed stratiform zinc orebody (Franklin, New Jersey, USA); with zeolites in leucitic lava (Capo di Bove, Italy). If you start seeing hedyphane, friedelite, pyrochroite in float, you are in the right ground. Typical habit: sphenoidal crystals, often twinned appearing pseudo-orthorhombic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify cahnite?+
Where is cahnite found?+
Is cahnite safe to handle?+
What rocks look like cahnite?+
What minerals are found with cahnite?+
What kind of rock does cahnite form in?+
What is cahnite used for?+
Find cahnite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
