Chrysoprase is a gemstone variety of chalcedony that contains small quantities of nickel. Its color is normally apple-green, but varies to deep green.
Chrysoprase is cryptocrystalline, which means that it is composed of crystals so fine that they cannot be seen as distinct particles under normal magnification. This sets it apart from rock crystal, amethyst, citrine, and the other varieties of crystalline quartz which are basically transparent and formed from easily recognized six-sided crystals. Other members of the cryptocrystalline silica family include agate, carnelian, and onyx. Unlike many non-transparent silica minerals, it is the color of chrysoprase, rather than any pattern of markings, that makes it desirable.