MINERALOGICAL MAGAZINE, VOLUME 62A Comparison of biotite dissolution in the laboratory and in the field by high-resolution transmission electron microscopy

The dissolution of minerals are generally explained by protonation, deprotonation a d the subsequent detach-ment of metal species (e.g. Stumm, 1992) based on laboratory experiments under 'far from equilibrium' conditions. The process is considered tobe applicable to the dissolution of sheet silicates in which Si and A1 ions dissolve from the edges of the 2:1 layers (e.g. Wieland and Stumm, 1992; Nagy, 1995). However, weathering in the field seems to be different from laboratory dissolution in terms of the saturation state with respect to primary minerals and the formation of secondary minerals. In particular, biotite weathering is usually accompanied by vermiculite overgrowth within a biotite grain (Banfield and Eggleton, 1988) partly because there is no significant difference