1. a hard crystalline mineral composed of magnesium aluminum oxide, often used as a gemstone
Usage: mineralogy

Examples

• The red spinel was often mistaken for ruby in ancient times.
• Spinel crystals form in octahedral shapes.
• The crown jewels include several large spinel gemstones.
• Blue spinel is rarer than the red variety.
• Synthetic spinel is commonly used in jewelry making.
• The mineral spinel has a hardness of 8 on the Mohs scale.