Thenardite

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Thenardite
Thenardite Sodium sulfate near Sodaville Mineral County Nevada.jpg
Sodaville, Mineral County, Nevada
General
Category Sulfate mineral
Formula
(repeating unit)
Na2SO4
Strunz classification 07.AC.25
Crystal symmetry Orthorhombic dipyramidal
H-M symbol: (2/m 2/m 2/m)
Space group: F ddd
Unit cell a = 5.86 Å, b = 12.3 Å, c = 9.82 Å; Z=8
Identification
Formula mass 142.04
Color White, grayish white, yellowish white, reddish white, brownish white
Crystal habit Forms crust-like prismatic aggregates on matrix
Crystal system Orthorhombic
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 grey 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.

Crystal structure of thenardite

References[edit]