A ruby is a pink to blood-red coloured gemstone , a variety of the mineral). Other varieties of gem-quality corundum are called sapphires. Ruby is one of the traditional cardinal gems , together with amethyst, and diamond The word ruby comes from ruber, Latin for red. The color of a ruby is due to the element chromium.
Some gemstones that are popularly or historically called rubies, such as the Black Prince's Ruby in the British Imperial State Crown. These were once known as "Balas rubies".
The quality of a ruby is determined by its color, cut, and clarity, which, along with carat weight, affect its value. The brightest and most valuable shade of red called blood-red or pigeon blood, commands a large premium over other rubies of similar quality. After color follows clarity: similar to diamonds, a clear stone will command a premium, but a ruby without any needle-like rutile may indicate that the stone has been treated. Ruby is the traditional birthstone, although some rhodolite garnets have a similar pinkish hue to most rubies. The world's most valuable ruby to be sold at auction is the Sunrise Ruby.