Thénardita y Mirabilita en precipitados químicos litorales de la laguna Mar Chiquita, Córdoba (Argentina)

BIGLIA, H. ; COLOMBO, F. ; PIOVANO E.; CÓRDOBA, F.

Mendoza

Congreso; 11 Congreso de Mineralogía y Metalogenia.; 2013

Asociación Mineralógica Argentina

Thénardite and mirabilite occur in a salt mud flat (30°56´20.43"S- 62°52´56.76"W) related to the Mar Chiquita hypersaline lake, the largest of its class in South America. Thénardite, NaSO4, occurs as crusts of euhedral colorless crystals reaching 2 mm, showing the forms {111} (dominant) and {010}, {101} and {011} (subordinate). Unit-cell dimensions refined from X-ray powder diffraction (XRPD) data are: a = 5.8631(4), b = 12.3126(7), c = 9.8223(7) Å, V = 709.07(8) Å3. The X-ray diagram shows an excellent match with the PDF file 1-70-1541. EDS spectra show only Na, O and S, with an Na:S ratio close to unity. Mirabilite was identified by XRPD, with a reasonable match with the PDF file 1-74-0937. Both minerals are associated to halite. The origin of these species is related to an influx of salty water from the lake to the freatic level, during the dry season (Winter and early Spring).