villiaumite

{{infobox mineral |boxtextcolor=|boxbgcolor=#c55e35| name = Villiaumite | category = Halide mineral | image = Villiaumite-t5128a.jpg | imagesize = 260px | alt = | caption = | formula = NaF | molweight = | strunz = 3.AA.20 | dana = | system = Cubic | class = Hexoctahedral (mm) H-M symbol: (4/m 2/m) | symmetry = Fmm (No. 225) | unit cell = a = 4.63 Å; Z = 4 | color = Carmine-red, lavender-pink to light orange | colour = | habit = Cubic crystals rare, commonly granular, massive | twinning = | cleavage = {001}, perfect | fracture = | tenacity = Brittle | mohs = 2 – 2.5 | luster = Vitreous | streak = White | diaphaneity = Transparent | gravity = 2.79 | density = | polish = | opticalprop = Isotropic; weak anomalous anisotropism, then uniaxial (–) | refractive = n = 1.327–1.328 | birefringence = | pleochroism = Strong E = yellow; O = pink to deep carmine | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence= dark red to orange and yellow fluorescence under SW and LW UV | absorption = | melt = | fusibility = | diagnostic = | solubility = Soluble in water | other = | alteration = | references = }} 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.

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