Montmorillonite with interstratified structure

Abstract

The action of magmatic vapors on andesitic rocks in the geothermal activity zone of Pathé, State of Hidalgo, Mexico, has produced a complex mineralogical association in which a dioctahedral montmorillonite interstratified with water layers is identified. The calculated formula is:
[(Si7.55Al0.45)(Al3.74Fe0.04Mg0.56)Mg0.18Ca0.33K0.02Na0.07]O20(OH)4,3.65°.

The interpretation of X-ray data, using the one-dimensional Fourier transformation, indicates probabilities of 0.48 and 0.52 for the montmorillonite and water layers, respectively, which do not strictly match the calculated formula. Infrared absorption analysis suggests abundant tetrahedral and octahedral substitution and lattice deformation, while electron micrographs show rolled crystalites approximately 0.2 x 0.04 microns. Chemical analyses of the magmatic vapor condensate, acting at 150°C and a pressure of 2.77 kg/cm², maintain a very humid environment at 270°C in the sampled vein.