Biotite - Hydrobiotite - Vermiculite in Soils

Abstract

IN the course of experiments dealing with the potassium chemistry of a group of alluvial and colluvial soils of California derived largely from weathering products of granite–diorite, we have observed the occurrence of minerals, presumably alteration products of biotite, which include trioctahedral vermiculite¹ and hydrobiotite^2,3 (regularly interstratified biotite–vermiculite). The minerals occur in some abundance in the fine sand, silt, and 0.5–2µ clay and are responsible for from 20–50 per cent of the cation-exchange capacity of the soils examined. A typical X-ray diffraction pattern for a magnesium–silt fraction, showing 25-Å and 12.5-Å peaks from hydrobiotite, 14.48 and 7.24 Å diffraction maxima from vermiculite and a 10.1-Å mica line is reproduced in Fig. 1A. Only 10.1-Å and 7.1-Å peaks were observed after saturation with potassium and air-drying, while sodium saturation resulted in peaks at 22.5, 12.3, 11.25, and 10.1 Å. Treatment of magnesium material with glycerol or ethylene glycol did not change peak positions.