spinel | mineral | Britannica
spinel, mineral composed of magnesium aluminum oxide (MgAl 2 O 4) or any member of a group of rock-forming minerals, all of which are metal oxides with the general composition AB 2 O 4, in which A may be magnesium, iron, zinc, manganese, or nickel; B may be aluminum, chromium, or iron; and O is oxygen.The spinel group is divided into three immiscible series: the spinel (aluminum-spinel) series ...