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