Abstract: Samples from kaolin deposits in the Dry Branch, Georgia, area were examined in oriented thin section, by X-ray diffraction, and as carefully disaggregated sand-sized grains. The object was to determine the orientation of kaolinite crystals with respect to any gross stratification in the deposits and with respect to their mineral precursors.
Large muscovite grains show a preferred horizontal orientation which produces a noticeable stratification in some soft kaolins in which they are relatively abundant. Interleaved kaolinite is oriented with its cleavage parallel to that of the remaining unaltered muscovite and is of the b-axis disordered variety. Pseudomorphs of kaolinite after feldspar occur in both the soft kaolins and the associated sandstones. These show no preferred orientation and are well-crystallized kaolinite. Authigenic kaolinite growing as vermicular “books” in the kaolin deposits and sandstones shows no preferred orientation direction and is well-crystallized also.
These observations lead to the conclusion that these Georgia kaolin deposits were not sedimented in still-standing waters as the mineral kaolinite. Major mineral constituents of the original sediment were muscovite and feldspar. Post-depositional alteration of these minerals has occurred as well as recrystallization of some of the kaolinite.