A group of minerals in which oxygen is combined with one or more metals to give simple and multiple oxides respectively. Simple oxides include hematite (Fe₂O₃), rutile (TiO₂), and zincite (ZnO). Multiple oxides include the spinels (MgAl₂O₄) and hydrated oxides, e.g. goethite (FeO.OH). Oxides are economically important and are the principal sources of tin (SnO₂), iron (Fe₂O₃, Fe₃O₄), chromium (FeCr₂O₄), titanium (TiO₂), manganese (MnO₂), and aluminium (Al₂O₃.2H₂O). Oxides are relatively high-temperature minerals occurring in association with a variety of igneous rocks. They may also form as chemical precipitates in oxidized environments.