Figure 10.02. MgO-SiO2 Norm Example #2: not enough SiO2. Consider another simple rock made of the two oxides, MgO and SiO2. This time the chemical anlysis of the rock finds 600 grams of MgO and 600 grams of SiO2, what will be the normative mineral percentages?

The same CIPW normative minerals (quartz, enstatite, and forsterite) are the ones that can be made from only MgO and SiO2. Converting the oxide values from mass units to mole units yields 15 moles of MgO and 10 moles of SiO2. In this case, if all the MgO is assigned to enstatite, there is not enough SiO2 to balance it. See the result by using the slider.