Black Prince's Ruby

The Black Prince's Ruby is currently set in the cross pattée in front of the Imperial State Crown, part of the Crown Jewels of England. Like many large red gems commonly called "rubies", it is in fact not a true ruby, but a spinel; the two gemstones can be distinguished on the basis of their hardnesses and densities, and the fact that a true ruby is dichroic while a spinel is singly refractive.

The stone was given to Edward the Black Prince by Pedro the Cruel, king of Castile, on the victory of Najera in 1367. It was worn by Henry V of England at the battle of Agincourt, and was almost lost there.