Villiaumite

Villiaumite
Small perfect crystal - Locality: Poudrette quarry, Mont Saint-Hilaire, Québec, Canada - field of view 1.4 x 1.4 mm
General
Category	Halide mineral
Formula (repeating unit)	NaF
Strunz classification	3.AA.20
Crystal system	Cubic
Crystal class	Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m)
Space group	Fd3m
Unit cell	a = 4.63 Å; Z = 4
Identification
Color	Carmine-red, lavender-pink to light orange
Crystal habit	Cubic crystals rare, commonly granular, massive
Cleavage	{001}, perfect
Tenacity	Brittle
Mohs scale hardness	2 - 2.5
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Specific gravity	2.79
Optical properties	Isotropic; weak anomalous anisotropism, then uniaxial (–)
Refractive index	n = 1.327–1.328
Pleochroism	Strong E = yellow; O = pink to deep carmine
Ultraviolet fluorescence	dark red to orange and yellow fluorescence under SW and LW UV
Solubility	Soluble in water
References

Villiaumite is a rare halide mineral composed of sodium fluoride, NaF. It is very soluble in water and some specimens fluoresce under long and short wave ultraviolet light. It has a Mohs hardness of 2.5 and is usually red, pink, or orange in color. It is toxic to humans.

The red color is due to a broad absorption peaking at 512 nm. It is a result of radiation damage to the crystal.

It occurs in nepheline syenite intrusives and in nepheline syenite pegmatites. It occurs associated with aegirine, sodalite, nepheline, neptunite, lamprophyllite, pectolite, serandite, eudialyte, ussingite, chkalovite and zeolites. It has been reported from Minas Gerais, Brazil; Mont Saint-Hilaire, Quebec, Canada; the Ilimaussaq complex of Greenland; Lake Magadi, Kenya; Windhoek District, Namibia; the Fen Complex, Telemark, Norway; the Khibiny and Lovozero Massifs, Kola Peninsula, Russia; Porphyry Mountain, Boulder County, Colorado and Point of Rocks Mesa, Colfax County, New Mexico, US.