Caracterização mineralógica do túnel da PCH Garça Branca e a primeira ocorrência de analcima no estado de Santa Catarina, Brasil

Abstract

Introduction: Different minerals have been found in the cavities of the volcanic rocks of the Serra Geral Group, Paraná Basin and in 2016, during the drilling of a tunnel for a dam in the municipality of Anchieta-SC, deltoid-icositerahedral crystals of analcime were found carpeting cavities and vesicles in the rocks, associated with other minerals. Objectives: Confirm the identity of the mineral as analcima and define the mineral facies in the extension of the tunnel. Methodology: Measurement of habit, dimensions, color, brightness, line, UV-L diffraction, density, loss to fire, cleavage, fracture, crosstalk, toughness and X-Ray difraction (DRX). Results: Isometric trapezoidal icosahedron habit with dimensions of up to five centimeters, colorless to white, translucent to opaque, vitreous luster, subconchoidal fracture, weak cleavage. In the muffle at 300ºC for 60 minutes it becomes white and friable. The average density is 2.26 g / cm³, Mohs hardness 5 to 5.5, white line, white color, loss of fire of 7.95% and X-ray with characteristic peaks for analcime. Discussion: Occurs in situ in five facies: Analcime and Mordenite / Scolecite (surface and included crystals); Euchral isolated analcimes up to 5 cm; Analcime and Estilbite-Ca with dissolution marks; Analcime and calcite with trigonal habit; Analcime and Stilbite-Ca euhedral, maclas and without dissolution. Conclusion: The tests performed confirmed the mineral species analcima (NaAlSi₂O₆.H₂O), being an important record of the occurrence in the State of Santa Catarina. 

Keywords: Mineralogy; Serra Geral; Zeolites; Facies; Crystals