Carletonite is an exceptionally rare phyllosilicate mineral known almost exclusively from the Poudrette quarry at Mont Saint-Hilaire. It is prized by collectors for its stunning blue color and well-formed tetragonal tabular crystals that often exhibit a pearly luster on cleavage surfaces.
Is this carletonite?
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 carletonite with a known reference. Carletonite sits at Mohs 4-4.5, 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 pearly, may become slightly waxy after long exposure to air.
- 4Match the color rangeCompare against the expected color range: colorless, light blue, dark blue, pink.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: prismatic.
Often confused with
Carletonite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside carletonite
Minerals reported to co-occur with carletonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KNa₄Ca₄Si₈O₁₈(CO₃)₄(F,OH)·H₂O
- Mohs hardness
- 4-4.5
- Density
- 2.45 g/cm³
- Streak
- White
- Luster
- Vitreous to pearly, may become slightly waxy after long exposure to air
- Transparency
- Transparent to translucent
- Crystal system
- Tetragonal
- Crystal habit
- Prismatic
- Cleavage
- Perfect on {001}, good on {110}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In cores of thermally metamorphosed wall-rock xenoliths of shale and interbedded limestone, now hornfels and siliceous marble, in nepheline syenite in an intrusive alkalic gabbro-syenite complex
Where rockhounds find carletonite
Classic worldwide localities
- Mont Saint-Hilaire, Quebec, Canada
Field-hunting tip
Where it forms: In cores of thermally metamorphosed wall-rock xenoliths of shale and interbedded limestone, now hornfels and siliceous marble, in nepheline syenite in an intrusive alkalic gabbro-syenite complex. If you start seeing quartz, narsarsukite, calcite in float, you are in the right ground. Typical habit: prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify carletonite?+
Where is carletonite found?+
What rocks look like carletonite?+
What minerals are found with carletonite?+
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Find carletonite on the map
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