Oxide

An oxide is a compound in which oxygen is combined with another element, usually with oxygen formally in oxidation state $-2$. Ionic metal oxides and covalent nonmetal oxides can have very different structures.

For example, magnesium oxide is a lattice solid, whereas carbon dioxide is molecular. Peroxides contain an oxygen-oxygen unit with a different oxidation-state assignment, so they should not be treated as ordinary oxides merely because they contain oxygen.

PbO2, with a formal Pb(IV) state. A common polymorph has a rutile-type extended structure with six-coordinate lead.

PbO, with a formal Pb(II) state and retained 6s2 pair. Its layered structures and asymmetric local environments contrast with a simple molecular monoxide model.

Magnetite is the iron oxide $\mathrm{F}{\mathrm{e}}_3{\mathrm{O}}_4$, commonly described as containing both iron(II) and iron(III) in an inverse-spinel structure. Its magnetic order is ferrimagnetic.

The unequal magnetic contributions of its sublattices leave a net magnetization. This makes magnetite a useful connection between oxidation-state chemistry, crystal structure, and bulk magnetism.

Titanium-bearing iron-oxide solid solutions related to magnetite, commonly important carriers of magnetization in igneous rocks.