Carletonite

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
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

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 was discovered by G.Y Chao and named for the school he attended, Carleton University of Ottawa. 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.

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.