Ilmenite’s ideal chemical composition is FeTiO₃. However, it often departs from that composition by containing variable amounts of magnesium or manganese. These elements substitute for iron in complete solid solution. A solid solution series exists between ilmenite (FeTiO₃) and geikielite (MgTiO₃). In this series, variable amounts of magnesium substitutes for iron in the mineral’s crystal structure. A second solid solution series exists between ilmenite and pyrophanite (MnTiO₃), with manganese substituting for iron. At high temperatures, a third solid solution series exists between ilmenite and hematite (Fe₂O₃).