Cumulate harzburgite is found in some large layered igneous intrusions. At the Earth's surface, basaltic magmas typically crystallize the minerals: olivine, plagioclase, and augite (a high-Ca pyroxene); low-Ca pyroxenes can only co-exist with olivine at low pressure in magma that is high in both MgO and SiO2 (boninites).
Cumulate harzburgite is found in some large layered igneous intrusions. At Earth's surface, basaltic magmas typically crystallize minerals: olivine, plagioclase, and augite (a high-Ca pyroxene); low-Ca pyroxenes can only coexist with olivine at low pressure in magma that is high in both MgO and SiO2 (boninites).