The Black Prince’s Ruby, approximately the same size as a chicken’s egg, is a bead-shaped gemstone weighing about 170 carats.
It is currently set in the Imperial State Crown above the Cullinan II. Of the crown jewels, it’s one of the oldest, dating back to the 14th Century when it was owned by its namesake, Edward of Woodstock, the Black Prince.
The referred to as a “ruby”, this gemstone is actually a spinel. More common than an actual ruby, spinels are not as hard or as dense as rubies. While not a ruby, however, it is the largest uncut spinel in the world, having never been properly cut.