Three hundred forty-three samples from so-called hard and soft kaolin deposits in the Atlantic Coastal Plain of Georgia and South Carolina were evaluated in terms of twenty-two chemical and mineralogical properties.

The purpose of this investigation was to obtain a better understanding of the origin and variability of the deposits. Samples were taken largely according to pre-determined sampling plans formulated to answer the questions, a) are the deposits homogeneous in terms of the measured properties and b) can the hard and the soft types be distinguished on the basis of these properties?

All variables tested by statistical methods are shown to be non-homogeneously distributed within the deposits. The hard and soft clay types can be distinguished by an analysis of variance in terms of the variables A12O3, Fe2O3 and kaolinite crystallinity; and possibly by several other variables which, although not shown to be statistically different, are strongly characteristic of one of the types. AI2O3 and crystallinity have greater values in the soft, and Fe2O3 has consistently higher values in the hard type. The larger particle sizes are associated with the soft type, and microscopic examination of thin sections shows that the hard type has feathery-patches of parallel-aligned flakes, in contrast to books interspersed in an isotropic matrix for the soft type.

In the soft type, positive correlations between Fe2O3 and mica, Fe2O3 and K2O, K2O and mica, and the negative correlations between mica and books, and Fe2C>3 and books, suggest that this type of clay may have been affected by leaching processes.

A possible explanation of the differences observed in the hard and soft kaolin deposits is that they were deposited in saline versus fresh water environments, respectively. The influx of a clay suspension into a saline environment resulted in a face-to-face type flocculation with attendant higher compaction, less permeability, and because of higher pH, more hydroxides of iron than would result from a fresh water environment. In the hard type the lack of permeability was because of relatively less recrystallization and crystal growth activity during and shortly after deposition. Similarly, this would account for less leaching action following uplift than was able to occur in the more permeable soft type.

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