The gemstone jade actually encompasses to different minerals - jadeite and nephrite. Both are extremely tough and both come in a variety of colors. A large volume of dark green nephrite is found in British Columbia. From there it is shipped over to China for cutting and then enters the world market.
Jadeite is often used for fine carvings because of it's toughness. 'A' Jade refers to jade that is untreated except for a light wax coating applied after the final polish. Although often purchased in Hong Kong or China, top quality jadeite always originates in Burma.
Black jade from Wyoming is sometimes used to replace black onyx in rings where breakage has been an issue.
Treatments: Usually waxed, often dyed.