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| Villiaumite | |
| Category: | Halide mineral |
| Formula: | NaF |
| Strunz: | 3.AA.20 |
| System: | Cubic |
| Class: | Hexoctahedral (mm) H-M symbol: (4/m 2/m) |
| Symmetry: | Fdm |
| Unit Cell: | a = 4.63 Å; Z = 4 |
| Color: | Carmine-red, lavender-pink to light orange |
| Habit: | Cubic crystals rare, commonly granular, massive |
| Cleavage: | , perfect |
| Tenacity: | Brittle |
| Mohs: | 2 – 2.5 |
| Luster: | Vitreous |
| Streak: | White |
| Diaphaneity: | Transparent |
| Gravity: | 2.79 |
| Opticalprop: | Isotropic; weak anomalous anisotropism, then uniaxial (–) |
| Refractive: | n = 1.327–1.328 |
| Pleochroism: | Strong E = yellow; O = pink to deep carmine |
| 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]
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, US.[2]
It was first described in 1908 for an occurrence in Los Islands, Guinea and named after the French explorer, Maxime Villiaume.[2]