BARRERITE TWINS, NEUQUEN PROVINCE, PATAGONIA, ARGENTINA

MARIA ELENA VATTUONE; LATORRE, CARLOS OSCAR; LEAL, PABLO

Santa Fe, EEUU

Congreso; 44° Annual Meeting of the Clay Mineral Society; 2007

Twinning barrerite belongs to a metamorphic assemblage of very low grade metamorphism in Paleogene metabasalts from the Andesitic Formation (40°46’/40°54’ S and 71°03’/71°07’ W). It was found in veins and amigdales with Ca-heulandite, tetranatrolite/Na-gonnardite, Ca-stilbite, stellerite and analcime which replace barrerite in the central parts of the veins. The twins of barrerite have not been described before. This sodic zeolite has grown by replacement of albite. Some colorless and transparent crystals of twin barrerite were found together with Ca-heulandite. In these rocks, barrerite shows crystals of above 0.5 cm long with {010}, {001}, {111}, {011} and {h0l} forms; cell parameters are a= 13.62 Å; b= 18.14 Å; c= 17.85Å; 2Vα = 80° and chemical analyses by EDAX show Si/Al ratio that ranges between 3.50 and 2.82. The thermic analyses indicate a water loss of 18% (Vattuone et al. 2001 a y b).