MgO-FeO-Na2O Ternary Diagram

Figure 3.02. MgO, FeO, and Na2O ternary diagram. Mass data are shown on this diagram for selected Hawaiian volcanic rocks from the PETROS Igneous Rock Database. Notice the inverse correllation between MgO and FeO at nearly constant Na2O, and the increase in Na2O as the amount of FeO decreases at low MgO.