STUDIES ON THE CLAY MINERALS OF MOUNTAIN SOILS IN HUBEI AND HUNAN PROVINCES I. THE CLAY MINERALS OF SOILS ON THE SOUTH SLOP OF THE DABIE MOUNTAINS

The association and chemical composition of clay mineral and cation exchange properties of 20 soil horizons in 7 soil profiles on the south slop of the Dabie Mountains in Hubei Province were studied. The results indicated that: 1). the 14(?) minerals and kaolinite were the main clay minerals in the soils examined, and the secondary was illite. The 14(?) clay mineral of soil on the feet of mountains was vermiculite. The content of vermiculite decreased whereas the content of 14(?) intergrade mineral in soils increased with the rising of the altitude. The chlorite was found in the middle and upper parts of the mountains. And with an rising of the altitude, the content of kaolinite decreased slightly but the degree of crystalinity was enhanced and the content of illite increased as well as a small ammount of 12(?) interstratified mineral was found. 2). the gibbsite was found in the subsoil at an altitude of 920m, then it not only was found in all horizons of soil profiles but also its ammount increased as the elevation was going up. 3). the chemical composition of soil clay fraction, even the surface chemical properties varied with the rising of altitude, which was quite agreeable to the change of clay minerals. 4). between the 14(?) clay minerals, vermiculite and 14(?) intergrade mineral in soils, there were apparent differences in their CEC, pH value and the ammount of exchangeable aluminum. The methods for identification of these minerals and the formation of gibbsite are discussed.