noun. a hard glassy mineral consisting of an oxide of magnesium and aluminum; occurs in various colors that are used as gemstones.
1. Noun, singular or mass A pure spinel is white, but is most often seen in many different colors, such as red, pink and black. 2. Noun, plural Many other gemstones like garnets, peridots, tourmalines, iolites, spinel and zircons fall between 6 and 7.5 on the hardness scale.
