Chrysoprase is one of the rarest and most valuable forms of chalcedony, which is a cryptocrystalline variety of quartz. ... It is coloured green by traces of nickel and its name derives from the Greek words chrysos, meaning gold, and prasos, meaning leek. Chrysoprase is one of the rarest and most valuable forms of chalcedony, which is a cryptocrystalline variety of quartz. It is coloured green by traces of nickel and its name derives from the Greek words chrysos, meaning gold, and prasos, meaning leek. In its finest form, this bright green ornamental gemstone has a glowing, ethereal quality. Chrysoprase possesses a soft translucence similar to an opal and an intense colour rivalling that of imperial Burmese jade; however, don’t be fooled, as it is a distinctly different mineral with unique properties.