Soil alteration processes on granite in the Central Mountain Range (Spain)

In the Central System of Spain exist outcrop of saprolites that are in a di spersive form in many zones. In this paper we study the evolution of the original granites to saprolite, which reaches a sandy stage, together with the selective alteration of fel dspars and micas. This paper is mainly concerned with the transformation ta king place in biotite during its weathering as observed in thin sections wi th the ligh microscope. Firstly micas altered to intergraded mid-vermiculit e, and subsequently into vermiculite and kaolinite. The degree of alteratio n increases as the size of the particle decrease.