The Definition and Classification of True Jade
     Based on archeological data, it has been shown that over several millenarian within the vast Pacific region, there appeared numerous cultures which venerated or worshipped jade. These include the Olmec and Mayan civilizations on the American continent and the Maori Culture of New Zealand, in addition to, of course, the age-old Chinese civilization. As the "jade" relics from these cultures were most often found to consist of nephrite or jadeite, minerologists have limited the scope of true jade to include only these two substances.

     Chemically speaking a silicate of calcium and magnesium, nephrite belongs to the amphibole group of minerals. It occurs primarily in dolomitic marbles or in serpentinized ultramafics. Throughout the ages, nephrite has been frequently employed as a working material. While the locations of the deposits that yielded very ancient nephritic jades aren't know, nephritic jades from the Shang Dynasty onward originate in dolomitic deposits of the Kunlun Mountains in Sinkiang Province. As it has been collected for the most part in the Ho-t'ien District, it has been called "Ho-t'ien jade." Nephrite of this provenance appears in numerous colors. From a snowy white state in the absence of impurities, it darkens into various shades of bluish white in relation to the amounts of magnesium or iron present. An increase in the amount of ferric ion imparts a yellowish hue. When particular areas of a piece of white or bluish-white jade contain hematite, brown jade is obtained; graphite infusions, depending on their concentration lead to either grey or black jade. The fact that these two colorations frequently coexist in a given stone had been exploited by the jade craftsman. Examples of jades whose coloration and shape harmonize can be seen in the "Cup in the shape of an animal horn" and the world renowned "Jade vase in the shape of a horned fish" displayed in National Palace Museum, Taipei.

     Dark-green nephrite has its origins in the serpentinized ultramafics of Sinkiang Province's Tien Shan Ma Na Ssu. Similarly colored nephrite has been quarried in Hualien on Taiwan, New Zealand, Canada, and elsewhere.

     A silicate of sodium and aluminum, jadeite is classed as a pyroxene. Although in a class different from nephrite, jadeite shares many characteristics with it, namely a high degree of hardness and firmness, and a luster that lends an appearance of transparency. Additionally, variations is iron content result in brownish-red, dark green, or lavender hues. Presence of minute amounts of chromium yields emerald green. Finally, the characters in the Chinese appellation for jadeite, fei-ts'ui, are those for two species of kingfisher whose feathers are of a color similar to that of brownish-red and emerald green jadeite.   

( extracted from exhibition catalogue of  National Palace Museum )




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