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common name for either of two minerals used as gems. The rarer variety of jade is jadeite, a sodium aluminum silicate, NaAl(SiO3)2, usually white or green in color; the green variety is the more valuable.
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(Greek nephros, “kidney”; in antiquity it was believed to be a remedy for kidney disease), a mineral variety of actinolite and tremolite, occurring as a compact microcrystalline aggregate with a minutely fibrous, felted structure. Extremely tough, nephrite readily acquires a polish. Its color varies from milky white or greenish to dark green, sometimes exhibiting mottled patterns owing to the inclusion of other minerals. It has been valued as a semiprecious stone since antiquity; tools and art objects have been fashioned out of it in various countries, particularly China, Burma, and India.
Nephrite is formed during the metamorphism of basic rocks, such as serpentinites and pyroxene and amphibole schists. It is generally extracted from alluvial deposits, where it occurs in the form of pebbles and large boulders. Major deposits of the mineral are found in the USSR (Vostochnyi Saian, the Baikal Region), China (Kunlun Mountains, basins of the Ho-t’ien and Yarkand rivers), New Zealand, and Polynesia.