There are two different minerals known as jade. They are “nephrite”, which is an amphibole, and “jadeite,” which is a pyroxene. Nephrite is the most common and widespread. It is formed of a mat of tightly interlocking fibers, creating a stone tougher than steel. It was used in China and New Zealand for tools and weapons due to its toughness. Its color varies with its composition dark green when iron-rich; cream colored when magnesium-rich.
The geologist A. G. Werner gave nephrite its name in 1780 from the word “nephrus,” meaning “kidney,” alluding to the use of this form of “jade” in Europe to treat kidney disease. The term “jade” evolved from the Spanish piedra de ijada, meaning “loin stone,” a stone of similar appearance to nephrite brought from the New World by the Spanish, which was, in fact, jadeite.
Nephrite is found in many locations around the world and is not often used in jewelry as much as jadeite. It is used mainly for carvings. It comes in fewer colors than jadeite, white (mutton fat jade), dull green (spinach jade) often with black spots of magnetite, brilliant green and yellow, which is the most valuable. Nephrite has a hardness of 6.5 (Mohs’ scale) and an SG of approximately 3.0. Nephrite is found in eastern Turkestan. Large deposits of nephrite are found on the Kobuk River in Alaska; in British Columbia, Canada; in Xinjing Autonomous Region, probably the original Chinese source; and near Lake Wakatipu, Otago, New Zealand, and the Maori source. It is also found in Lander, Wyoming, Mariposa and Siskiyou counties, and in Monterrey and Morro Bays, California; in the Lake Baikal area of Siberia; and in Ch’unch’on, South Korea. In addition, it is found in Australia, Mexico, Brazil, Taiwan, Zimbabwe, Italy, Poland, Germany, and Switzerland.
Most of the early Chinese jade carvings are of nephrite which was probably imported from Central Asia. It was not until the eighteenth century that jadeite from Burma was introduced, and it is the most important source of jadeite today. Burmese jadeite is found in metamorphic rocks and also as alluvial boulders. The boulders have a brown skin which is due to weathering. Jadeite and nephrite are used as cabochons, in other jewelry, and for vases both decorative and religious. The main cutting centers are in China as well as Taiwan and Hong Kong.