Plots of CaO/MgO (wt % ratio) versus CaO/FeO (wt % ratio) for (A) all holohyaline edge and center data from 15426 and 74220. In (B) are shown only the 15426 data with subgroupings by Delano (1979) displayed. Data obtained from 15426 180 spans all groupings except for Group 15C.