What is "spinel"

Spinel \Spi*nel"\, Spinelle \Spi*nelle"\, n. [F. spinelle, or LL. spinellus, perhaps from L. spina a thorn, a prickle, in allusion to its pointed crystals.] (Min.) A mineral occuring in octahedrons of great hardness and various colors, as red, green, blue, brown, and black, the red variety being the gem spinel ruby. It consist essentially of alumina and magnesia, but commonly contains iron and sometimes also chromium.

Note: The spinel group includes spinel proper, also magnetite, chromite, franklinite, gahnite, etc., all of which may be regarded as composed of a sesquioxide and a protoxide in equal proportions.

Spinel \Spin"el\, n. Bleached yarn in making the linen tape called inkle; unwrought inkle.
--Knight.

n. (context mineralogy English) Any of several hard minerals of cubic symmetry that are mixed oxides of magnesium and aluminium and are used as gemstones of various colours.

n. a hard glassy mineral consisting of an oxide of magnesium and aluminum; occurs in various colors that are used as gemstones

Spinel is the magnesium aluminium member of the larger spinel group of minerals. It has the formula MgAlO in the cubic crystal system. Its name comes from Latin "spina" (arrow). Balas ruby is an old name for a rose-tinted variety.