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

Carletonite
Carletonite, Poudrette quarry, Mont Saint-Hilaire, Montérégie, Quebec, Canada
General
Category	Phyllosilicate
Formula (repeating unit)	KNa4Ca4(CO3)4Si8O18(F,OH)·(H2O)
IMA symbol	Cto[1]
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
Identification
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 - 4+1⁄2
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	[2][3][4][5]

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 was discovered by G.Y Chao and named for the school he attended, Carleton University of Ottawa.^[6] 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.^[3][4]

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.^[3]