Spinel is the magnesium aluminium member of the large spinel group of minerals. Spinel occurs in an array of colors. Its wide and varied palette of colorless, black, red, yellow-orange, green, blue, and purple-purple.

For the first time the name "spinel" was used in the book "De natura fossilium" ("On the Nature of Minerals") by the German scientist Georgius Agricola (Georg Bauer, 1494-1555) in 1546. He singled out this mineral from a common series of "carbuncles" based on hardness and Lustera. And the name spinel came to be used in 1797 by Martin Klaproth (Martin Heinrich Klaproth, 1743-1817). There is no information on the origin of the name. Different researchers derive the name from different languages respectively, and with different meanings.

The mineralogical varieties depending on the crystal formula are as follows:

- Pleonast is an intermediate member of the "spinel-hercinite" group. The black color of this variety of spinel is due to the presence of the isomorphic admixture of Fe2+ in Mg2+ position.

- Automolite (gahnospinel) is an intermediate member of the "spinel-ganit" group. The blue and green colors are due to the presence of Zn2+ in Mg2+ position, as well as by small amounts of impurity Fe2+, Fe3+, Cr3+, Mn2+, Mn3+, Ni2+, Co2+ and possibly others.

- Sometimes the structure is referred to as a "chrome spinel" that is a chrome variety, which is an intermediate member of the "spinel-picrochromite" group and is black mainly.

There are many more compounds with a spinel structure but that do not form isomorphous series of complete mixing.

Chemistry: MgAl2O4;

Crystal system: Cubic, hexoctahedral crystal class (point symmetry group);

Color: The color of spinel is due to the presence of isomorphic impurities of the elements of chromophores in the crystal lattice of the mineral and their correlation. Thus, the red color of the "ruby spinel" is caused by the isomorphous impurity of Cr3+, the pink color of the "ball-spinel" is Cr3+ and/or V3+, the "almandine spinel" is Fe2+ (Cr3+ and/or V3+can participate in its coloration). Other colors can be caused by the complex impact of various groups of impurity ions. Fe2+ and Fe3+ ions participate in the formation of green, blue and violet and purple colors, for example, the Zn2+ ions play a decisive role in the green and blue color of the autolithite (gahnospinel), in complex with Fe2+ and/or Fe3+ ions. Blue ions can also be determined by Co2+ ions and a complex (Ti4+, Fe2+, and Сr3+).

Identification properties

Physical properties
Mohs hardness: 7.5-8

3.54 – 3.65 g/cm3;

3.63 – 3.90 g/cm3 (for pleonast);

4.00 – 4.06 g/cm3 (for gahnospinel);

Cleavage: imperfect on (111)
Fracture: uneven, conchoidal
Optical properties
Optical character: isotropic, anomalous, anisotropy
Refractive Index:

1.712 – 1.762;

1.712 – 1.810 (for pleonast and gahnospinel)
Birefringence: none, anomalous - poor
Pleochroism: none
Dispertion: 0,020(BG)
Luster: vitreous

Inclusions and structural inhomogeneities

Mineral inclusions