Sodaville, Mineral County, Nevada
Category Sulfate mineral
(repeating unit)
Strunz classification 7.AC.25
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Fddd
Unit cell a = 5.86 Å, b = 12.3 Å
c = 9.82 Å; Z = 8
Formula mass 142.04 g/mol
Color White, grayish white, yellowish white, reddish white, brownish white
Crystal habit Forms crust-like prismatic aggregates on matrix
Twinning Interpenetration twinning on {001}; also on {100}
Cleavage {010} Perfect
Fracture Splintery
Tenacity Brittle
Mohs scale hardness 2.5
Luster Vitreous to resinous
Streak White
Diaphaneity Transparent
Specific gravity 2.67–2.7, average = 2.68
Optical properties Biaxial (+)
Refractive index nα = 1.471, nβ = 1.477, nγ = 1.484
Birefringence δ = 0.013
Pleochroism none
2V angle 83°
Ultraviolet fluorescence Fluorescent and phosphorescent: short UV=bright white, long UV=bright white
Solubility Soluble in water
Other characteristics Salty taste
References [1][2][3]

Thenardite is an anhydrous sodium sulfate mineral, Na2SO4 which occurs in arid evaporite environments. It also occurs in dry caves and old mine workings as an efflorescence and as a crusty sublimate deposit around fumaroles. It occurs in volcanic caves on Mt. Etna, Italy. It was first described in 1825 for an occurrence in the Espartinas Saltworks, Ciempozuelos, Madrid, Spain and was named for the French chemist, Louis Jacques Thénard (1777–1826).[2]

Thenardite crystallizes in the orthorhombic system and often forms yellowish, reddish to gray white prismatic crystals although usually in massive crust deposits. Thenardite is fluorescent, white in shortwave and yellow-green in longwave UV radiation.

In humid conditions, thenardite gradually absorbs water and converts to the mineral mirabilite, Na2SO4·10H2O.


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