| The composing of clay minerals of aggregate of red soil soils derived from Quaternary red clay and the effect of clay in aggregate formation process with different erosion and aggregate stability was discussed by investigating their physical and chemical properties in this paper. The main results were showed in following:1)The clay minerals of the samples from ChangSha (Hunan province), XianNing and ChiBi (Hubei province) mainly were composed of kaolinite, hydromica and 1.4nm intergrade minerals. The amounts of clay minerals, Fed and Ald content, PZC,SSA and CEC of the soil samples increased with the increase of erosion degree.2)The amount of pore and percent of pores in the samples decreased with the increase of erosion degree, and the water stablility of micro-aggregate also increased with the increase of erosion degree. Water-stable aggregates＞0.25 mm (WSA) and mean-weighted diameter (MWD), which can indicate the stability of aggregate, were positively and significantly correlated with clay content. The correlation coefficients were 0.79 (p＜0.01 n=22) and 0.73 (p＜0.01 n=22). WSA and MWD were also significantly correlated with Fed and Ald content with the correlation coefficient 0.73 (p＜0.01 n=22), 0.72 (p＜0.01 n=22) and 0.72 (p＜0.01 n=22), 0.70 (p＜0.01 n=22)。But poor correlation was observed between WSA, MWD and Feo, Alo.3)The amounts of Fed and Ald in the exterior of the aggregate exterior were higher than that of in interior. And the average of Feex-Fein was 1.34mg/g,1.16mg/g and 1.55mg/g in the soil samples from ChiBi, XianNing and ChangSha, respectively. The average of Alex -Alin were 0.86mg/g, 0.42mg/g and 1.11mg/g in the soil samples from ChiBi, XianNing and ChangSha respectively. The margin of average of Feex -Fein between serious and light erosion was largest in tested aggregates from XianNing soil samples. The margin of average of Alex -Alin between serious and light erosion was largest in the tested aggregates from XianNing soil samples. Serious eluviation causes the difference of Fe and Al oxides content in aggregate interior and exterior. Preferential weathering of aggregate surfaces caused a shift from strongly bound to other Fe and Al forms and preferential sorption of deposited Fe and Al on the aggregate surfaces resulted in a total enrichment of Fe and Al oxide in the aggregate exteriors.4)The amount of 1.4 nm intergrade mineral and kaolinite in the exterior was higher than that of the interior of tested aggregate in most soil samples from XianNing and ChiBi (HuBei province). However, the amount of hydromica in these samples was contrary. The margin of amount of theses mineral between exterior and interior was significant increased with the increase of erosion degree. Maybe, parent material, weathering condition and environment factors caused this difference.The mineral in the exterior easily changed into unexpand and more satbility kind, such as kaolinite. And Al enrichment caused decrease of pH which vailed to form 1.4 nm intergrade mineral. More rainfall influenced the form and transform of hydromica which content in the exterio was less than in the interior.5)SEM data clearly showed that the morphology of the microaggregate of different erosion was different. The rotundity or ellipse and little edge could be observed in Microaggregate under going serious erosion. These may be caused by water eroding in long time. And the morphology of light erosion microaggregat was contrast to that of serious erosion samples.6)The Fe oxide uniformity distributed in the microaggregate, and the amount of Fe oxide in edge part was higher than that of middle part, and the difference was more significant in the serious erosion samples. The enrichment of Fe oxide in edge part was more significant in some edge points. These results showed that Fe oxide act as a "bridge" action when two microaggregate connected to form large aggregate.
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