A type of rock that, owing to its origin from the decomposition of various constituent minerals, varies considerably in appearance and characteristics. The most valuable varieties are of shades of green, resembling and sometimes sold as the nephrite variety of jade; and some bear misnomers, e.g. Korean jade and new jade. Often it is mottled with reddish-brown, hence its name. It is fairly soft, so that it has been used for carving cameos and intaglios.
A harder variety is bowenite, which is more used in jewelry than are the other varieties, e.g. Williansite, Antigorite, Retinalite. Massive rocks of serpentine include several varieties of marble, and fibrous serpentine (chrysotile) is a source of asbestos.
From: An Illustrated Dictionary of Jewelry, autor: Harold Newman, publishers: Thames and Hudson