ABSTRACT

Authigenic kaolinite in sandstone occurs most commonly as fragile aggregates of crystals. It is present in interstices between grains, in cavities and vugs, along fractures, and as grains. These types of occurrence indicate that authigenic kaolinite may form by crystallization from solution, by alteration in place of some parent mineral, and by recrystallization of fine-grained, detrital kaolinite minerals.

Reported occurrences are from sandstones of Ordovician to Miocene age, of several petrographic types, and of various depositional environments. Garnet, staurolite, feldspar, and apparently quartz, to a lesser extent, are unstable under kaolinite-forming conditions. Since some of these conditions are apparently realized by fresh or brackish ground water moving through a sandstone, salinity maps of a reservoir offer a means of predicting the occurrence of secondary kaolinite in it.