Weathering of Biotite: Micro to Nano Scale Reactions in the Regolith

INTRODUCTION The chemical and physical weathering of minerals is the fundamental process giving rise to much of the regolith and affects critical processes of the regolith such as metal release and retardation (dissolution-precipitation) and adsorption. Although our understanding of mineral weathering reactions for most primary minerals is extensive from a unit cell scale (Hochella & Banfield 1995), knowledge of micro environments on mineral weathering remains limited. The processes and products of weathering of biotite has been extensively studied both in the laboratory and in under natural conditions with the type of end products considered to be dictated by the conditions experienced by the soil such as acidic, leached or waterlogged (Wilson 2004). The main mechanism is considered to be the oxidation of Fe in the mica with subsequent release of K from the interlayers to form “hydrobiotite” and subsequently vermiculite, which involves only a structural adjustment. Further release of K as solution access increases results in the formation of kaolinite and goethite, with studies finding different alteration products such kaolinite or halloysite and goethite. However, the biotite weathering investigations do not consider the weathering products on microsites within individual biotite grains, and each biotite grain and the regolith unit in which it is weathering potentially has a story to tell on weathering reactions and products. The aim of this article is to investigate the different mechanisms and products that arise in different microsites within a weathering profile evolved on a granodiorite.