SOIL COLLOID RESEARCHES Ⅸ. COMPARISON OF CLAY MINERAL IN TWO PAIRS OF YELLOW EARTHS AND RED EARTHS IN GUANGDONG PROVINCE
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Abstract:
The clay mineral composition of two pairs of yellow earth and red earth derived from granite in Quangdong were analysed qualitatively and quantitatively by X-ray and chemical methods.In the profiles of two red earths,the composition of clay mineral in the fraction <2 μm varied insignificantly,containing about 50-55% kaolinite,20% amorphous materials and gibbsite and small amount of hydromicas,mixed-layer mineral and mineral of 14Å.In addition,the whole profile of red earth in Jianfengling still contained small amount of smectite.On the contrary,the composition of clay minerals of yellow earth differed from that of red earth,which contained more mineral of 14Å and hydromica,with less kaolinite.However,the composition of clay mineral of two yellow earths also varied greatly.The yellow earth with lower weathering degree taken from Yangchun contained mainly mineral of 14Å and hydromica,its kaolinite content less than 15%;while the yellow earth with higher weathering degree taken from Jianfengling contained mainly kaolinite,being as much as 40%,but still contained a certain amount of minerals of 14Å and hydromica.Smectite was not found in the solum of these two yellow earths,only small amount of smectite was discovered in regolith of granite.Mineral of 14Å in the yellow earth belonged to intergradient mineral,that is vermiculite with unegchangeable hydrozy-Al interlayer.Due to organic matter in the surface soil hydrosy-Al interlayer will be removed easily,which indicates that organic matter is unfavourable for the formation of hydroxy-Al interlayer in swelling mineral.The granite residual materials of yellow earths contained much more halloysite,less kaolinite and a certain amount of gibbeite.Besides,there also existed some smectite and calcite in granite residual materials of Yangchun,this indicated that smectite may be formed in the early weathering stage of granite,if calcium exist.
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