Villiaumite

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Villiaumite
Villiaumite1 - Poudrette quarry, Mont Saint-Hilaire, Quebec, Canada.jpg
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 03.AA.20
Crystal symmetry Isometric 4/m 3 2/m
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
Crystal system Cubic hexoctahedral
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 [1][2][3]

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.[2]

The red color is due to a broad absorption peaking at 512 nm. It is a result of radiation damage to the crystal.[4]

Occurrence[edit]

Villiaumite, (field of view 7.1 x 4.7 mm), Poudrette quarry, Mont Saint-Hilaire, Quebec, Canada

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.[1] 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, USA.[2]

It was first described in 1908 for an occurrence in Los Islands, Guinea and named after the French explorer, Maxime Villiaume.[2]

See also[edit]

References[edit]