Inheritance and formation of smectite in a texture contrast soil in the Pilliga State Forests, New South Wales

Smectite genesis is generally considered to require an alkaline environment, for in acid environments it is reportedly unstable. This study shows that smectite is forming in an acid, texture-contrast soil in the Pilliga State Forests in north-western New South Wales. Three modes of smectite genesis in the study soil are presented. The first mode involves direct inheritance from the underlying parent rock. The second and third modes involve precipitation of smectite from solution and its deposition from suspension, respectively. While the bulk of the smectite in the study soil is inherited from the transformation of labile primary minerals and rock fragments in the parent rock, restricted drainage coupled with a parent material capable of supplying the elemental constituents of smectite are also important factors in its genesis.