The sillimanite-patash felspar-quarzt shists and the muscovite-quartz schists of Hitachi District are quite similar in chemical composition, though different in mineralogical composition. The difference is represented by the equation below; muscovite + quartz ⇆ orthoclase + sillimanite + water ↑ The right side of this equation is considered to represent the higher facies by TURNUR(1951), RAMBERG(1952) and others. The boundry between the distribution areas of these two rocks shows the different form from that of the ordinary cases. It looks like the flame of a candle. These both rocks are metasomatic. Besides them, some kinds of metasomatic rocks are also recongnized, and there are the differences in mineralogical composition, which represent the difference in P.T. conditions, among them. The form of fhe boundary lines are also like the flame of a candle. The non-metasomatized amphibolites and felsic schists in the area of the sillimanite-potash felsperquartz schists are not differnt from those in the area of the muscovite-quartz schists. Two ways of thinking are possible from these facts. The first way is that there might be the real difference in the P.T. condition between the sillimanite-potash felsper-euartz schist and the muscovite-quartz. But on this assumption we must consider the amphibolite, accompanied by the sillimanite-potash felsper-quartz schists, to have the relictic mineral association. The second way is that no difference in the P.T. condition is assumed between these two, but the difference in the concentration of volatiles in rocks, because of the different metasomatic condition, seems to have existed. The difference brought the different mineral associations even in the same P-T conditions, as shown by the YODER's experiments. The present author takes the second way of thinking.
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