Ruby

A ruby is a pink to blood-red colored gemstone, a variety of the mineral corundum (aluminium oxide). The red color is caused mainly by the presence of the element chromium. Its name comes from ruber, Latin for red. Other varieties of gem-quality corundum are called sapphires. Ruby is considered one of the four precious stones, together with sapphire, emerald and diamond.

Prices of rubies are primarily determined by color.The brightest and most valuable "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 inclusions may indicate that the stone has been treated. Cut and carat (weight) are also an important factor in determining the price. Ruby is the traditional birthstone for July and is always lighter red or pink than garnet. The world's most expensive ruby is the Sunrise Ruby.

https://en.wikipedia.org/wiki/Ruby