Occurrence and Origin of Crystalline Iron Oxides in Paddy Soils Derived from Red Earth

红壤性水稻土晶态氧化铁主要为针铁矿，并伴随少量的赤铁矿．红壤性水稻土中针铁矿的铝同晶替代量明显低于其母土（红壤），而针铁矿的晶胞参数ｂ和ｃ则是红壤性水稻土高于其母土．红壤性水稻土中赤铁矿的铝同晶替代量和晶胞参数ａ则与其母土相似．．据此认为红壤性水稻土中赤铁矿来源于母土；而针铁矿部分来源于母土，部分是由原有的赤铁矿和针铁矿的还原产物重新结晶形成的．随着水稻土的发育，赤铁矿逐渐下降，最后消失；针铁矿则相对增加，同时针铁矿中铝替代量也逐渐下降

Occurrence and Origin of Crystalline Iron Oxides in Paddy Soils Derived from Red Earth

Crystalline iron oxides in paddy soils,derived from red earths,were essentially goethite,and accompanied by small amounts of hematite.The amount of Al isomorphous substitution of goethite in these paddy soils were obviously lower than those in their corresponding parent soils.However,the amount of Al isomorphous substitution and the value of unit cell dimension a of hematite in those paddy soils were similar to their corresponding parent soils.It might suggested that hematite in the paddy soils derived from red earths was inherited from parent soils.However,goethite in those soils were partly relict from red earths,and partly recrystallized from some reduction products of original hematite or goethite.With the development of paddy soils,the amount of hematite in the soils decreased and finally disappeared,and goethite increased relatively.Meanwhile,the amount of Al substitution in goethite also decreased gradually.