From the field inspection of weathered granitic rocks, we divided them into following five zones; the outermost part with a characteristic of talus and the inner transitional four parts for weathered zone.
The degrees of the alteration of biotite and the production of secondary minerals in the process of weathering are roughly parallel to the degree in progress of weathering. The weathered biotites collected from each zone indicated the variation of basal reflection (001) from 10Å to 11-14Å with production of the hydrous or hydrated minerals such as hydrobiotite and 14Å mineral (vermiculite) and sometimes associated with certain amount of goethite derived from the dissolved iron. A lot of 14Å mineral is Al rich vermiculite. The latest products are the aluminous minerals such as kaolinite and/or gibbsite derived from vermiculite. While in some specimens, kaolinite was recognized in biotite in the initial step of weathering.

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Recently weathered granitic rocks from several localities of northeast, central, and southwest Japan were examined mineralogically, with special reference to kaolinite and halloysite. The result obtained is that long tubular halloysite is predominant in the weak weathered part, while highly disordered kaolinite increases with decrease of halloysite in the intensely weathered part. From this result, it is concluded that granitic rocks alter to kaolinite by weathering, either immediately or through halloysite as an intermediate product.
Clay mineral composition of the Pliocene sediments and their basement granite, which has been reported previously, was discussed comparing with the recently weathered granitic rocks, the conclusion being that the diagenetic transformation between kaolinite and halloysite is not important. Moreover, kaolinite in Palaeogene sediments at the Iwate mine, northeast Japan, was compared with that in the beforementioned Pliocene sediments. It is concluded from this comparison that kaolinite in sediments of the older geologic age has higher structural regularity than that in the younger sediments.

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The properties of interlayer or nonexchangeable potassium in micaceous minerals obtained from two soils were examined as compared with that of muscovite, 2M-type dioctahedral mica, and sericite, 1M-type one, by following methods: with sodium tetraphenylborate (NaTPB) solution, and molten lithium nitrate, interlayer potassium was extractedfrom minerals and changes of thier basal spacing were observed by X-ray diffraction analysis.
With both treatment, interlayer potassium of soil minerals was released more difficult than that of sericite, but so easy as that of muscovite. However, the mode of potassium release from soil minerals was rather similar to the case of muscovite. The result of X-ray diffraction analysis also showed the similarity between soil minerals and muscovite, but changes of the basal spacing in soil minerals seemed to be slightly diffused by co-existance of 2: 1 type minerals such as vermiculite.
Above results suggest that mica minerals in soils may be 2M-type dioctahedral micas. They have remained for a long time because of the strong stability against soil weathering reactions.

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