Figure 2.22. Fe-Mg Zoning in Olivine Crystal from an Andesite. The forsterite content as a function of distance across a relatively equant, small olivine crystal in an andesite is shown as a red line. This relatively symmetrical compositional profile was measured by Costa and Chakraborty (2007) on an olivine grain from an andesite lava erupted from Volcán San Pedro in the Chilean Andes.