Chrysoprase

Chrysoprase is a gem variety of chalcedony, the cryptocrystalline form of silica, coloured green by traces of nickel held in very small inclusions; emerald, by contrast, owes its green to chromium. Its usual shade is apple green, though it ranges from a cyan close to turquoise to a deep green, and darker stones are sometimes called prase. The name joins the Greek words for gold and green. Its grains are too fine to pick out even under ordinary magnification, which separates it from crystalline quartzes such as amethyst and citrine, and it is valued for its colour rather than for any markings. It forms where nickel-bearing serpentinite and similar rocks have weathered deeply; well-known sources include Queensland and Western Australia, Tanzania, Poland and Brazil. Like other chalcedony it has a Mohs hardness of between 6 and 7. Cunningham assigns chrysoprase to Venus, to earth and to the goddess Vesta, and has it worn for luck, success, friendship and protection, to drive off greed and envy, and to keep nightmares away. Hall links it with deep meditation, love of truth, creativity, fidelity and forgiveness, and with peaceful sleep and fertility. The healing claims both authors make for it are theirs, not established medicine.