Thénardite

Anhydrous sodium sulfate mineral
(repeating unit)Na2SO4IMA symbolThn[1]Strunz classification7.AC.25Crystal systemOrthorhombicCrystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)Space groupFdddUnit cella = 5.86 Å, b = 12.3 Å
c = 9.82 Å; Z = 8IdentificationFormula mass142.04 g/molColorWhite, grayish white, yellowish white, reddish white, brownish whiteCrystal habitForms crust-like prismatic aggregates on matrixTwinningInterpenetration twinning on {001}; also on {100}; common on {110}; {011}Cleavage{010} perfect, {101} fair, {100} incompleteFractureSplintery, uneven, hacklyTenacityBrittleMohs scale hardness2.5LusterVitreous to resinousStreakWhiteDiaphaneityTransparentSpecific gravity2.67–2.7, average = 2.68Optical propertiesBiaxial (+)Refractive indexnα = 1.471, nβ = 1.477, nγ = 1.484Birefringenceδ = 0.013Pleochroismnone2V angle83°Ultraviolet fluorescenceFluorescent and phosphorescent: short UV=bright white, long UV=yellow-greenSolubilitySoluble in waterOther characteristicsSalty tasteReferences[2][3][4]

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 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, thénardite progressively absorbs water and converts to the deca-hydrated mineral mirabilite, Na2SO4 · 10 H2O.

  • Crystal structure of thénardite
    Crystal structure of thénardite
  • Thénardite, cluster of transparent crystals from Soda Lake, California. Width of cluser is 9 cm (3.5 in).
    Thénardite, cluster of transparent crystals from Soda Lake, California. Width of cluser is 9 cm (3.5 in).
  • Tan thénardite pseudomorphing mirabilite crystals from the Boron, California area. Cluster is 6 × 5.5 cm.
    Tan thénardite pseudomorphing mirabilite crystals from the Boron, California area. Cluster is 6 × 5.5 cm.

References

Wikimedia Commons has media related to Thénardite.
  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Thénardite at Webmineral
  3. ^ a b Thénardite at Mindat
  4. ^ Handbook of Mineralogy

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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