The word “phenomenal” has a special use in gemology. The name is used for gems that have a special optical reaction to light. Some specimens of spinel contain a network of thousands of needle-shaped crystals of rutile that reflect light from specific directions. In some specimens of spinel, these reflections produce a six-ray star when the gem is cut en cabochon.

The blue spinel in the photo is an example of a spinel cabochon with a six-ray star. These phenomenal gems are known as “star spinels.”