The above diagram shows pyroxene minerals. These plot in the three component system Enstatite (En) - MgSiO3, Wollastonite (Wo) - CaSiO3, Ferrosilite (Fs) - FeSiO3. Wo does not have a pyroxene structure Complete solid solution exists between Diopside, Di, (CaMgSi2O6) and Hedenbergite, Hd, (CaFeSi2O6). These pyroxenes are monoclinic and are thus called the clinopyroxenes. Augite is also a clinopyroxene, but note that it is depleted in the Wo component relative to the Di - Hd series. En - Fs also forms a complete solid solution series. These minerals are orthorhombic, so the series is often referred to the orthopyroxenes. Pigeonite (named after Pigeon Point, Minnesota, USA) is a monoclinic pyroxene that has slightly more of the Wo component than the orthopyroxenes.