Scanning electron micrographs of contracts of feldspar weathering to kaolin minerals show the formation of at least two morphologies of kaolin-a platy, book type and an elongate, halloysite type. The morphology of an elongate kaolin mineral, hitherto not illustrated, is micro-graphed. Kaolin minerals are interpreted as originating from a solution phase intermediate between parent feldspar and daughter kaolin. Platy, book-type kaolinite is interpreted as forming under geologic conditions of a “weathering crust, ” which geochemical conditions persisted essentially at equilibrium over a very long time. Elongate kaolin minerals apparently form under relatively higher land conditions, and/or where kaolinization was governed by shorter time kinetic processes.

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