The origins of kaolinite-rich rocks associated with coal measures in China

Kaolinite-rich rocks are widespread in Chinese coal-bearing strata. Three m ain types of deposits are recognized. Those deposits identified as flint cl ays are several metres thick and show lateral variations in bed composition . The kaolinite is thought to have formed mainly on the adjacent landmass, but some crystallization of gels within the basin is not ruled out. Tonstei ns, which formed from the in situ alteration of airfall volcanic ashes, are very common in the coal measures and are up to 0.5 in thick. Finally, kaol inite deposits are described where the development of kaolin is related to weathering of coals either close to or at the present land surface.