Villiaumite

Villiaumite
General
CategoryHalide mineral
Formula
(repeating unit)
NaF
Strunz classification3.AA.20
Crystal systemCubic
Crystal classHexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space groupFd3m
Unit cella = 4.63 Å; Z = 4
Identification
ColorCarmine-red, lavender-pink to light orange
Crystal habitCubic crystals rare, commonly granular, massive
Cleavage{001}, perfect
TenacityBrittle
Mohs scale hardness2 – 2.5
LusterVitreous
StreakWhite
DiaphaneityTransparent
Specific gravity2.79
Optical propertiesIsotropic; weak anomalous anisotropism, then uniaxial (–)
Refractive indexn = 1.327–1.328
PleochroismStrong E = yellow; O = pink to deep carmine
Ultraviolet fluorescencedark red to orange and yellow fluorescence under SW and LW UV
SolubilitySoluble 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]

  1. ^ Handbook of Mineralogy
  2. ^ a b Mindat.org
  3. ^ Webmineral
  4. ^ "Villiaumite Visible Spectra (350 – 1050 nm)". Archived from the original on 3 December 2013. Retrieved 29 May 2013.