Biotitization of vermiculite under hydrothermal condition

Abstract

Hydrothermal experiment was carried out reacting vermiculite with K- and Si-bearing solutions in a Teflon vessel at 150°C for 14, 51, and 71 days to demonstrate biotitization of vermiculite. Our results revealed that biotite is formed within 71 days. High-resolution transmission microscopy and energy dispersive X-ray spectrometry showed that biotite is formed by precipitation directly from solution, domain formation in vermiculite, layer-by-layer transformation of vermiculite, or combination of the three. Our results clearly indicate that biotitization of vermiculite occurs under hydrothermal condition when K is available. Our study suggests that vermiculite formed during weathering is altered progressively to biotite by diagenesis as well as metamorphism after burial.