Rough Nephrite Jade
This stone is known as nephrite, because in early times it was used in amulets against kidney disorders. Both jadeite and nephrite are known as jade, so the term nephrite jade rather than merely nephrite, will be used hereto distinguish between the two. Although it is one of the two types of minerals which are fully entitled to be called jade. nephrite jade is less highly prized nowadays than jadeite jade, which
more often has strong, attractive colors. But nephrite iade was very important in ancient Oriental art, especially in China, where fine objects were fashioned from it up until the mid~eighteenth century. the use of jadeite jade only being established after that period.
Appearance It is generally found in fairly homogeneous
opaque to translucent masses, which are a fairly strong but not very lively green. However. the color can be dark green to blackish. gray or blue-gray. Grayish white is also very common. lt may contain brown. yellow-brown or orange streaks of iron oxide. Because of its exceptional toughness. it is used for the carving of figurines. bas-reliefs. and elaborate, thin-walled vases. It is also made into necklace begds and pendants and, much more rarely. cabochons an engraved pieces tor setting in jewelry. it takes a good polish. Pale. slightly translucent and not too lustrous specimens have a greasy or waxy appearance that is characteristic oi much antique Chinese jade.
Distinctive features It is distinguished from jadeite jade by its felted, rather than granular, structure. as well as its lower density and different refractive indices (although these are hard to establish). It is mainly distinguished by its density. but also by its greater hardness, from some varieties of serpentine, which look very similar to the more translucent type. It is also distinguished by its density from certain rocks containing hydrogrossular and vesuvianite which are often translucent and very similar. These are known as Transvaal or Pakistan jade. depending on their place of origin.
Occurrence Nephrite jade is fairly widespread, so much so that it was used virtually everywhere by Neolithic man for polished stone weapons. The chief sources are the Soviet Union (Turkeslan, Siberia) and New Zealand. It is also found in Canada, the United States. and Australia.
Value On the whole, it is of very modest value, being widely used for necklaces and other items of modern jewelry; but its extraordinary mechanical properties and particular appearance have been exploited (generally by Oriental craftsmen) to produce works of art of outstanding aesthetic value and complexity of detail, such as loose chains with unjointed links: small vases intricately entwined with fantastic dragons and often having handles with loose chains hanging from them; bells with moving clappers. which work as well as metal ones; and minutely engraved knife or weapon handles. Such items are valuable and where artistic merit is combined with antiquity, nephrite fetches extremely high prices.
Simulants and synthetics An imitation of nephrite jade consisting of a paste, recrystallized to form a translucent material with felted or fascicular zones of crystals, has been produced in Japan in recent years. This has a lower density (ca. 2.65 g/oma) than nephrite jade and a refractive index of about 1.53. It is known as imori stone or metajade. Natural materials such as aventurine. serpentine. andthe polycrystalline mixtures of hydrogrossular and vesuvianite look very similar, at first glance. to nephrite jade. and are used as substitutes. These are called jade, preceded by their place of origin, i.e.. lndian jade, Korean jade, Transvaaljade, respectively. Such names are considered an abuse of proper gemolcgical terminology. These materials have interesting ornamental properties, but their value is lower than that of nephritejade, and lower stiil than jadeite jade. Synthetic nephrite is not produced.