ETYM French spinelle, or Late Lat. spinellus, perhaps from Latin spina a thorn, a prickle, in allusion to its pointed crystals.
A hard glassy mineral consisting of an oxide of magnesium and aluminum; occurs in various colors that are used as gemstones.
rubylike precious stone.
Any of a group of “mixed oxide” minerals consisting mainly of the oxides of magnesium and aluminum, MgAl2O4 and FeAl2O4. Spinels crystallize in the cubic system, forming octahedral crystals. They are found in high-temperature igneous and metamorphic rocks. The aluminum oxide spinel contains gem varieties, such as the ruby spinels of Sri Lanka and Myanmar (Burma).