The kaolinite tonstein in the seam 5# is formed by acidic ash alterated in the acid medium in peat bog in tongchuan district.

• 铜川矿区5%23煤层中的高岭石泥岩夹矸是由酸性火山灰在近地表的成煤条件下经酸性水淋滤、蚀变而成的。