Mixed‐layer Biotite‐chlorite Formed in the Course of Local Epigenesis in the Weathering Crust of a Biotite Gneiss

Abstract

SUMMARY In the course of deep weathering of a biotite gneiss, biotite is transformed into mixed‐layer biotite‐vermiculite hydrobiotite. Later biotite‐vermiculite is transformed into biotite‐chlorite under the action of hydrothermal solutions at the stage of epigenesis.

Geochemical chaos: Periodic and nonperiodic growth of mixed-layer phyllosilicates

“…Periodic layer stacking has been reported for various series of phyllosilicates: illite-smectite (e.g., Nadeau et al, 1984;Ahn and Peacor, 1986;Eberl et al, 1990;Veblen et al, 1990), chlorite-talc (Schreyer et al, 1982), chlorite-pyrophyllite (Kong et al, 1990), smectite-illite (Veblen et al, 1990), chlorite-smectite (Hiller, 1993), chlorite-serpentine (Bailey et al, 1995;, smectite-pyrophyllite (Dong et al, 2002), and chlorite-biotite (Eroshchev-Shak, 1970;. In contrast, nonperiodically interstratified silicate layers, not considered as independent mineral species, have received less attention, although their occurrences are probably more abundant than the periodic ones (e.g., .…”