Villiaumite | |
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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 | [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]