Fig. 62.-Euhedral biotite (chloritized) with complicated muscovite

The upper right border of an euhedral biotite (Bi) changed to chlorite (Chl) is somewhat destroyed by muscovite. The latter can be divided into two parts (Ms and Ms single prime). Ms outside Bi is primary, while Ms single prime inside Bi is formed by nibble replacement. It is still difficult to judge which one occur earlier, co-orientation chloritization or hetero-orientation muscovitization. As a general rule, the author postulates that the nibble muscovitization should have occurred prior to the co-orientation chloritization.