Iron-Bearing Olivines and Pyroxenes

In this chapter, we continue to examine the effects of adding iron to simple magnesian systems. As expected, we shall find that Fe lowers the melting temperatures appreciably, but in addition we find that fundamental changes occur in the reaction relation of olivine to pyroxene. The chapter opens with a review of the system MgO-FeO-SiO2, taken in part from the original research paper. It then continues with an iron-bearing version of Fo-An-SiO2, the effect of adding oxygen to MgO-FeO-SiO2, a discussion of quadrilateral pyroxenes and their evolution, and silica activity in magmatic systems.