Figure 6. Selected biotite compositions are plotted in the "ideal biotite plane" diagram of Guidotti (1984). Biotite end-members are shown for comparison. Arbitrary division between phlogopites and biotites (Mg:Fe = 2:1) are taken from Deer et al. (1966).

Figure 6. Selected biotite compositions are plotted in the "ideal biotite plane" diagram of Guidotti (1984). Biotite end-members are shown for comparison. Arbitrary division between phlogopites and biotites (Mg:Fe = 2:1) are taken from Deer et al. (1966).