Jasper is a grainy variety of chalcedony. The name comes from the Greek iaspis or "spotted stone." Jasper has been used as a gemstone since Biblical times and may be one of the stones mentioned in the Breastplate of Aaron. There are numerous varieties of Jasper. These are sold under various trade names which have not been completely standardised. Red jasper is one the more common types although many gemologists believe that iaspis originally referred to green jasper, which is extremely rare. Jasper is also used to imitate other gemstones such as jade.