Thénardite

Thénardite is an anhydrous sodium sulfate mineral, Na2SO4 which occurs in arid evaporite environments, specifically lakes and playas. 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 Mount 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).[3]

Thénardite
Sodaville, Mineral County, Nevada
General
CategorySulfate mineral
Formula
(repeating unit)
Na2SO4
IMA symbolThn[1]
Strunz classification7.AC.25
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupFddd
Unit cella = 5.86 Å, b = 12.3 Å
c = 9.82 Å; Z = 8
Identification
Formula mass142.04 g/mol
ColorWhite, grayish white, yellowish white, reddish white, brownish white
Crystal habitForms crust-like prismatic aggregates on matrix
TwinningInterpenetration twinning on {001}; also on {100}; common on {110}; {011}
Cleavage{010} perfect, {101} fair, {100} incomplete
FractureSplintery, uneven, hackly
TenacityBrittle
Mohs scale hardness2.5
LusterVitreous to resinous
StreakWhite
DiaphaneityTransparent
Specific gravity2.67–2.7, average = 2.68
Optical propertiesBiaxial (+)
Refractive indexnα = 1.471, nβ = 1.477, nγ = 1.484
Birefringenceδ = 0.013
Pleochroismnone
2V angle83°
Ultraviolet fluorescenceFluorescent and phosphorescent: short UV=bright white, long UV=yellow-green
SolubilitySoluble in water
Other characteristicsSalty taste
References[2][3][4]

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

In humid conditions, thenardite progressively absorbs water and converts to the deca-hydrated mineral mirabilite, Na2SO4 · 10 H2O.

References

Bibliography

  • Palache, P.; Berman H.; Frondel, C. (1960). "Dana's System of Mineralogy, Volume II: Halides, Nitrates, Borates, Carbonates, Sulfates, Phosphates, Arsenates, Tungstates, Molybdates, Etc. (Seventh Edition)" John Wiley and Sons, Inc., New York, pp. 404-407.
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