The unique appearance of tiger's eye is caused by fibrous inclusions that have been replaced by silica. Light is refracted from inclusions, giving tiger's eye its chatoyancy (changeable luster).
Traditionally carried as an amulet, lustrous tiger's eye was thought to help make decisions and promote harmony and balance. It was also thought to aid in eye health. Associated with self-confidence and courage, tiger's eye is usually cut as a cabochon.
A type of quartz, tiger's eye is usually yellow-orange to darker brown or grey. Bull's eye (mahogany) and hawk's eye (bluish-grey) are alternate colors with their own descriptive names, but all still quartz.
Tiger's eye is not the same mineral as Cat's Eye chrysoberyl. It has a Mohs hardness rating of 7, making it a good choice for most jewelry styles.