Feldspar grains or their pseudomorphs from the different weathering zones are studied with the SEM. Weathering commences with dissolution to form voids in the grains. Close to the rock, the first product is allophanic material present as globules adhering to the voids in the grains. In the δ zone the product is halloysite with some amorphous silica spherules. The surface of the pseudomorph has a hummocky appearance suggesting an amorphous intermediary phase prior to halloysite formation. Kaolinite formation commences in the γp zone and gibbsite in the γm zone. Admixtures of kaolinite and halloysite may be found on the same pseudomorph, but admixture of gibbsite with another secondary mineral is not encountered.Biotite follows a similar trend of alteration. It is concluded that irrespective of the primary weatherable mineral, the type of secondary mineral found is a function of the microenvironment.

To facilitate description and study, the deep profile is divided into several morphological zones, via., α, γm, γp and δ zones. Clay content progressively increases from the rock zone δ to the soil zone α. The silt/clay ratio increases from the δ to the upper part of the γp zone and then decreases again. These changes are explained in terms of the fragmentation or aggregation of various minerals during the clay separation procedure. Estimates of the mineralogical composition in the fine earth shows differences in the zones, and the charge characteristics are related to these.Changes in the microfabric are monitored with thin‐sections. Micrographs are presented showing fabric characteristics and some examples of pseudomorphic alteration. A brief discussion on the genesis of the profile is given.

Different minerals characterize the three fractions in the different weathering zones. Halloysite in the clay fraction especially in the α and γ zones is due to a physical comminution of silt‐sized tubes. Strong peaks for halloysite (XRD) in the silt and sand fractions in these zones is shown (SEM) to be from partly altered feldspar fragments. Gibbsite is present mainly in the fine‐silt size and its presence in the sand in the α zone is due to cementation and aggregate formation. Aggregation of kaolinite also results in its being present in the silt and sand fractions.Estimates of the minerals in the three fractions are shown diagramatically as depth functions. XRD diffractograms of the three fractions and TEM micrographs of the clay fraction are also presented. It is concluded that the morphologically identified weathering zones also differ in their mineralogical properties.