A Ruby displaying asterism is known as a “Star Ruby”, and if transparent can be very highly prized. Star Rubies exists in six ray stars, though twelve ray stars are also well known. Rubies must be having good transparency to possess gem value. Opaque or semi-opaque Rubies have relatively little value, even if they display asterism.
The color of Ruby is usually caused by minute inclusions of the metal chromium. These impurities are often responsible for causing a Ruby to be fluorescent, which can be helpful in its identification. Ruby is also pleochroic, and will sometimes display a lighter and more intense color when viewed at different angles.
Despite this, Ruby is still subject to chipping and fracture if handled roughly, and care should be taken to ensure it is properly handled.