The ruby, birthstone for July, is among the most highly prized of gemstones.
Large rubies are harder to find than large diamonds, emeralds and sapphires.
As a result, rubies' value increases with size more than any other gemstone. Ancient Orientals believed that the ruby was self-luminous. It's said that an Emperor of China once used a large ruby to light his chamber, where it glowed as bright as day. Along with its close relative, the sapphire, the ruby is a form of the mineral corundum, which is normally drab and grey in color. Red gemstone corundum is called ruby.