Thenardite
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).