A kind of white clay rock similar to grog matericals is found in Early Carboniferous coal seams in northern Shanxi. here it is called "Burned kaoli- nite clay rock",because it is formed by the metamorphism spontaneous com- bastion of the coal. Studies with microscope and electron microscope, chemical analysis, diffe- rential thermal analysis as well as X-ray diffraction analysis etc., reveal that the clay rock consists of metakaolinite with mullite or kaolinite, locally with epigenetic allophane.