Throughout history, people believed most Spinels to be Rubies. It wasn’t until 1783 when meteorologist Jean Baptiste Louise Rome de Lisle determined that Spinels are in fact different than Rubies. Spinels were just recently added as an August birthstone joining Peridot and Sardonyx.
The most valued Spinels are vivid reds and cobalt blues. Other colors are pink, mauve, lilac, and black.
The lighter pastel colors are expected to be mostly free of inclusions, but the deeper more saturated colors (the reds and blues) are expected to have inclusions. Some of inclusions can appear to resemble human fingerprints.
The spinel is most often cut in cushion and oval shapes.
Spinels are commonly cut to standard sizes for jewelry. Spinels are also suitable for stones in rings as they measure around 6x4-mm and 7x5-mm in size.