Spinel
Definition and meaning of Spinel in chemistry.
Spinel is a class of crystalline inorganic compounds with the general formula AB2O4, where A is typically a divalent metal cation (such as Mg2+ or Zn2+) and B is a trivalent metal cation (such as Al3+ or Cr3+). The term also describes the characteristic cubic crystal structure that these compounds adopt.
In more detail
In the spinel crystal structure, oxygen anions form a face-centered cubic framework with metal cations occupying specific tetrahedral and octahedral voids. The prototype and most well-known spinel is magnesium aluminate (MgAl2O4); the pure, stoichiometric compound is colorless, though gem-quality natural spinel crystals are often vividly colored (red, pink, blue, or violet) due to trace transition-metal impurities such as Cr3+, Fe2+/3+, or Co2+. The spinel structure type is significant in materials chemistry because many industrially important oxides adopt this arrangement, including magnetite (Fe3O4), a ferrimagnetic iron ore. Spinels are valued for applications ranging from gemstones to catalytic materials and refractory compounds.
Key facts
| General Formula | AB2O4 (A = divalent metal; B = trivalent metal) |
|---|---|
| Prototype Compound | MgAl2O4 (magnesium aluminate) |
| Crystal System | Cubic |
| Field | Inorganic Chemistry |
Magnetite (Fe3O4) is a classic example of a spinel-structured compound; it exhibits strong ferrimagnetism and is mined as a major ore of iron.
Frequently asked questions
Is all spinel MgAl2O4?
No. MgAl2O4 is the prototype, but other metal combinations form spinels with the same crystal structure, such as magnetite (Fe3O4) and zinc aluminate (ZnAl2O4).
Why is spinel structure important in chemistry?
The spinel structure is adopted by many useful compounds in catalysis, materials science, and mineralogy. Understanding the structure helps predict and design compounds with desired properties.