Fig. 11. Harker diagram showing trend of data for MgO wt. % versus SiO₂ wt. % in the Gray's School granite and related amphibolite and biotite-rich gneisses. Data are from Carl and deLorraine (1997) and Table 1. Small solid diamond = granite samples analyzed by Carl and deLorraine; solid triangle = paired samples of biotite-hornblende amphibolite (77A) and granite (77B); solid circle = biotite-hornblende amphibolite (64 & 89); solid square = biotite gneiss (82 & 85) paired with granite (84).