Ruby is the red variety of corundum, an aluminum oxide with a hardness of 9. Its intense red color, which comes from chromium, has a vibrancy unsurpassed in the mineral kingdom. Inclusions of rutile (titanium dioxide) can cause light diffusion in cabochon cut stones, creating a six pointed star. Ancient Burmese legend held that inserting a ruby into one's flesh would make that person invulnerable. The Chinese emperor, Kublai Khan, was said to have offered an entire city in exchange for a huge ruby. They can impart a feeling of power to the wearer, improving self-confidence and adventurousness. Rubies are mined in Sri Lanka, Burma, Thailand, India, Brazil, and the United States.