Rubies, the birthstone of July, are precious gemstones composed of corundum, chromium bonded with aluminum oxide. Corundum comes in a variety of colors, but when it is red, it is always a ruby. Blue or pink varieties of corundum are always referred to as sapphires, though some disputes exist about whether pink sapphire is merely a lighter colored ruby.

Most rubies are mined in Myanmar, formerly Burma, and other parts of Asia and Africa. Some high quality rubies have recently been found in Kenya. A few US states, Montana and the Carolinas, have also discovered rubies, but most of the best gems are found in Myanmar.