Chrysoprase, chrysophrase or chrysoprasus is a gemstone variety of chalcedony (a cryptocrystalline form of silica) that contains trace amounts of nickel which gives the Chrysoprase its green color. Chrysoprase is composed of crystals so fine that they cannot be seen as distinct particles under normal magnification. This sets it apart from rock crystals. Ancient Greek, Romans and Egyptians used chrysoprase in jewellery and other ornamental objects, and due to its semi-opaque green colour it is often mistaken for imperial jadeite.