Another magnificent spinel in the Crown Jewels is known as the Black Prince Ruby. At 170 carats, the Black Prince Ruby rests in the front center of the Imperial State Crown, signifying its importance. Because spinel was often mistaken for other jewels, it has few legendary attributes or associations with magical powers. One tale, however, describes spinel as useful in detecting persons with supernatural powers. Clairvoyants were found guilty as charged, if, when approached with a spinel wrapped in paper, they began to shake.
Spinel occurs in all colors, often in subdued hues or with a slightly grayish overcast.
Pure red is the most popular spinel color and is caused by traces of chromium in its molecular structure. Chromium is also the coloring agent in ruby and pink sapphire. Violet colors are attributed to traces of manganese, while iron accounts for the blue hues, similar to sapphire. The limited supply and thus rarity of spinel accounts for its status as one the gem world's best kept secrets, and yet it is far more affordable than its look-alike, ruby. Top grade red spinels often sell for a fraction of the cost of a ruby of comparable size and quality.