Clay minerals formed from micas and chlorites in some New Zealand soils

Abstract

Clay mineralogical differences between eight soils in South Island, New Zealand, are related to differences in climate, vegetation, and formation time. Alteration of chlorite follows the sequence chlorite→interlayered hydrousmica→chlorite-swelling chlorite→chlorite-vermiculite, with increased weathering leading to the destruction of the chloritic layers. Mica (muscovite) follows two alteration sequences depending on the overlying vegetation. Under tussock grassland the sequence is mica→mica-vermiculite→mica-beidellite→beidellite. This sequence is also followed under beech forest, together with the sequence of mica→vermiculite→beidellite, with pedogenic chlorite forming when the pH is > 4·5. All but one of the interstratified products (the interlayered hydrous mica) appear to be based on a 1:1 regular interlayering of the two components.