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Carletonite, 1.0 x 0.7 x 0.6 cm, Poudrette quarry, Mont Saint-Hilaire, Montérégie, Quebec, Canada.
Category Phyllosilicate
(repeating unit)
Strunz classification 9.EB.20
Crystal system Tetragonal
Crystal class Ditetragonal dipyramidal (4/mmm)
H–M symbol: (4/m 2/m 2/m)
Space group P4/mbm
Unit cell a = 13.17 Å, c = 16.69 Å; Z = 4
Colour Colourless, light blue, dark blue, or pink
Crystal habit Prismatic crystals, massive
Cleavage Perfect on {001}, good on {110}
Fracture Conchoidal
Tenacity Brittle
Mohs scale hardness 4 - 4½
Lustre Vitreous
Streak White
Diaphaneity Transparent to translucent
Specific gravity 2.45
Optical properties Uniaxial (-)
Refractive index nω = 1.521 nε = 1.517
Birefringence δ = 0.004
Pleochroism Weak; O = pale blue; E = pale pinkish brown
References [1][2][3][4]

Carletonite is a rare silicate mineral with formula KNa4Ca4(CO3)4Si8O18(F,OH)·(H2O).

It is a phyllosilicate and a member of the apophyllite group. Its tetragonal crystals are a translucent blue, white, colorless or pink with a vitreous to dull lustre. It has a density of 2.45 and a hardness of 4-4.5.

It is named after Carleton University, in Ottawa, Ontario. It was first described in 1969 for an occurrence at Mont Saint-Hilaire, Quebec. The type locality at Mont Saint–Hilaire is the only reported occurrence.[2][3] It occurs in hornfels and siliceous marble xenoliths within and adjacent to a nepheline syenite intrusion. It occurs in association with quartz, narsarsukite, calcite, fluorite, ancylite, molybdenite, leucosphenite, lorenzenite, galena, albite, pectolite, apophyllite, leifite, microcline and arfvedsonite.[2]