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One-third of the world's and most US kaolin is produced from Late Cretaceous and Early Tertiary sedimentary strata in Georgia and South Carolina. The kaolin is part of a belt extending to Arkansas of aluminous lateritic deposits, including bauxite. Original sediments were profoundly altered by chemical weathering during Early Tertiary time.
Mining exploits those uncommon deposits where extreme leaching and chemical recombination have produced a clay of nearly pure mineral kaolinite. Properly selected and refined, kaolin is an important pigment, filler, extender and chemical compound in the paper, paint, plastics, ceramics and catalyst industries.
Kaolin
Commercial US kaolin products are selected or well-refined white powdery clays. They consist mostly of platy, commonly pseudohexagonal crystals about 2 microns or less in diameter of kaolinite (Fig. 1). The consistent analytical composition of the kaolinite component of 39.5% A1203, 46.5% SiO2 and 14% H20 usually is only diluted by impurities of about 1% anatase (TiO2) and 0.5% iron oxides. Quartz and white mica occasionally are present. Products intended for ceramic applications can contain significant montmorillonite or gibbsite.
Raw kaolin as mined can contain greater quantities of impurities. In some, large vermiform crystals of kaolinite are present (Fig. 2) that can be up to 2 mm (0.08 in.) long. Halloysite or metahalloysite are also found. Most mined kaolin is white but reddish to yellowish and gray clays comprise a portion of raw feed stocks.
Geologists see an even wider range of properties. There exist kaolins of almost any color. Quartz sand and mica components can exceed the kaolinite. Other impurities include pyrite, iron oxides, gibbsite and montmorillonite. They make an estimated 95 % of explored kaolin unsuited for processing.
Geological setting Kaolin regions. Commercial deposits of kaolin occur in the southeastern US Coastal Plain from South Carolina west to Arkansas (Fig. 3). They are remnants of ancient lateritic soils that formed near Early Tertiary shorelines. They are coincident with bauxite, which is also present. A small volume of kaolin is mined in central Florida from Miocene kaolinitic sands.
Kaolins of the Early Tertiary coast. Kaolin is present within and has formed from the Late Cretaceous and Early Tertiary strata and older intrusive rocks. Study of the bauxites by the US Bureau of Mines during World War II (Overstreet, 1964)...