Sesquioxide clays are common in tropical regions where temperature and rainfall are high. There would be high leaching of bases resulting in the formation of acidic soils. Higher the sesquioxides, more the soil is coarse and light. 1:1 type silicate clays are also found in tropical regions that have low CEC, pH dependent charges and less surface area. On the contrary, the 2:1 silicate clays are abundant in temperate and sub tropical regions which have high base saturation leading to high pH. Now the doubt in my mind is that at given base saturation, what should be the order of pH values with respect to different clay minerals.

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