thénardite

{{Infobox mineral | name = Thénardite | category = Sulfate mineral | boxwidth = | boxbgcolor = | image = Thenardite Sodium sulfate near Sodaville Mineral County Nevada.jpg | caption = Thénardite from Sodaville, Nevada | formula = Na2SO4 | IMAsymbol = Thn | molweight = 142.04 g/mol | strunz = 7.AC.25 | dana = | system = Orthorhombic | class = Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) | symmetry = Fddd | unit cell = a = 5.86 Å, b = 12.3 Å c = 9.82 Å; Z = 8 | color = White, grayish white, yellowish white, reddish white, brownish white | habit = Forms crust-like prismatic aggregates on matrix | twinning = Interpenetration twinning on {001}; also on {100}; common on {110}; {011} | cleavage = {010} perfect, {101} fair, {100} incomplete | fracture = Splintery, uneven, hackly | tenacity = Brittle | mohs = 2.5 | luster = Vitreous to resinous | refractive = nα = 1.471, nβ = 1.477, nγ = 1.484 | opticalprop = Biaxial (+) | 2V = 83° | birefringence = δ = 0.013 | pleochroism = none | streak = White | gravity = 2.67–2.7, average = 2.68 | density = | melt = | fusibility = | diagnostic = | solubility = Soluble in water | diaphaneity = Transparent | other = Salty taste | fluorescence = Fluorescent and phosphorescent: short UV=bright white, long UV=yellow-green | references = }}

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 in Ciempozuelos, Spain, by the Spanish chemist José Luis Casaseca (1800 - 1869). Casaseca named the mineral after his master, the French chemist Louis Jacques Thénard (1777–1857).