spi·nel also spi·nelle 
(spĭ-nĕl)
(spĭ-nĕl)n.
1. A hard, variously colored mineral with composition MgAl2O4, having usually octahedral crystals, occurring in igneous and metamorphosed carbonate rocks, and valued as a gem. The red variety is sometimes confused with ruby.
2. Any of a group of minerals that are oxides of magnesium, iron, zinc, manganese, or aluminum.
[Italian spinella, diminutive of spina, thorn (from its sharply pointed crystals), from Latin spīna.]