Resumen de Minerais dos grupos pirite e marcasite: cristaloquimica e propiedades fisicas dos compostos de ferro
M. O. Figueiredo, M. J. Basto, Aurelio Álvarez Pérez, J. L. Briansó
A synopsis is presented on the crystalchemistry of the basic M X2 crystal-structure types «pyrite» and «marcasite», and corresponding derivatives by distortion and/or anionic ordering. Geometric and topologic aspects accounting for changes in the state of chemical bonding are analised, namely the geometry of anionic ordering. Geometric and topologic aspects accounting for changes in the state of chemical bonding are analised, namely the geometry of anionic and cationic coordination polyhedra, X - X and M - M interatomic distances, and unit anionic volume. For the iron minerals (pyrite, marcasite, ferroselite, fróhbergite, lollingite, seinajdkite, arsenopyrite and gudmundite), some interesting correlations were found between the reported crystalchemical parameters and changes in physical properties-like microhardness, reflectivity and density as a function of the chemical nature of the anion and of the crystal-structure type assumed by the mineral.
