Named after the compound spinel, MgAl₂O₄, which consists of AlO₆ octahedra with aluminum in the center, and MgO₄ tetrahedra with Mg in the center. Two of the three cations in this structure will be found in octahedral sites, while the remaining one will be found in a tetrahedral site. The determination of which cation enters which coordination can be found from examining the crystal field stabilization energy (it is not dictated by ionic radius). Almost any mineral may be made into a spinel structure. Normal spinels are spinel structures in which identical cations occupy octahedral sites.

Inverse spinels have octahedral sites are shared by the two cations. An example is magnetite, which has formula Fe⁺³[Fe⁺²Fe⁺³]O₄.