Occurrence and morphology of goethitized pyrites in the county of Formiga – MG

Abstract

Introduction: The pseudomorphs of goethite after pyrite occur in the sedimentary domain of the Bambuí Group, having a cubic habit, octahedral, dodecahedral, combinations of these and forming globular spheroidal aggregates. Objectives: To gauge morphological, mineralogical and dimensional data. Methodology: 1352 globular samples were collected in three localities and their diameters, habits, internal structure, trace and density were measured using a pachymeter, camera, stereoscope microscope and analytical balance. Results: Average density of 3.55 g / cm3, with loss of 42.04% for the original sulfide (5.01 g / cm3), cubic and octahedral habit in isolated crystals and globular aggregates, porous nucleus and reddish yellow , reddish-yellow trait, mean diameter of the globular aggregates of 19.97 mm and standard deviation 8.22 mm. Conclusion: They are restricted to the Bambuí Group, presenting different degrees of pseudomorphosis, dimensions below 88.06 mm and habits subordinate to the biochemical conditions of each occurrence, with predominance of the cube, secondarily octahedral and combined forms of these, with crystallizations of different generations.