The term jade refers to two different minerals -- jadeite and nephrite.
Chemical composition -- Sodium aluminum silicate.
Color -- A wide range of colors including white, green, yellow, red, orange, violet, and black.
Optics -- R.I. 1.64-1.67. Usually the refractometer shows only one line near 1.66.
Durability -- Hardness 6.5-7. Very tough.
Crystal structure -- Monoclinic, usually massive.
Specific gravity -- 3.25-3.36.
Sources -- Major sources include Burma, New Zealand, Guatemala, and Siberia. Prized for carvings, frequently from China. The finest green Imperial jade is very rare and expensive.
Chemical composition -- A fibrous variety of the amphibole mineral series actinolite to tremolite, usually closer to actinolite.
Color -- Green, black, brown, beige (mutton-fat jade). Usually darker and less intense colors than those of jadeite.
Optics -- R.I 1.62.
Durability -- Hardness 6-6.5. Extremely tough, except when its composition approaches that of tremolite.
Crystal structure -- Monoclinic , usually massive.
Specific gravity -- 2.9-3.0.
Sources -- Many sources, including Chinese Turkestan, Taiwan, New Zealand, Wyoming, Lake Baikal, British Columbia, and California. Prized for centuries in Chinese carvings.