Nephrite is a mineral with a hardness of 7 out of 10 on the Mohs scale of mineral hardness [?]. These Monoclinicly structured gems are made of calcium magnesium iron silicate, their full chemical compound being Ca2(Mg,Fe)5Si3O22(OH)2.
Nephrite is a silicate of calcium, magnesium, and iron, containing fluorine and hydroxyl. It is an amphibole of the actinolite series. It occurs in all colors, also striped and spotted, but the most valuable color is green.
The amphiboles of the tremolite-actinolite series usually occur as elongated, parallel, radiating, or even fibrous crystals; but the variety known as nephrite has a very compact, felted, microcrystalline structure, which gives it the extreme tenacity characteristic of jade. The color varies from pale or whitish for the magnesium end-member, to darkish green for members with a high iron content.
The relatively easy cleavage of the amphibole group is not found in this microcrystalline material.
Nephrite is more common than jadeite jade, but it is distinguished by its felted, rather than granular structure, as well as its lower density and different refractive indices. It is also distinguished 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 source.
Nephrite jade 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. It may contain brown, yellow-brown, or orange streaks of iron oxide.
It occurs in both contact and regionally metamorphosed iron and magnesium-rich rocks.
The amphiboles of this series are relatively common minerals, widely distributed in the metamorphic and basic magmatic rocks.
The chief sources are Turkestan, Siberia, and New Zealand. It is also found in Canada, USA, and Tasmania (Australia). It is found in the west of Sinkiang (China), near Kashgar and Khutan in serpentinite and in river pebbles. On the west end of Baikal Lake, there is a spinach- green variety (Russian jade). Further deposits are in Burma, Brazil, Mexico, New Guinea, Taiwan, and Poland.
Nephrite (Jade) can be confused with agalmatolite, amazonite, aventurine, bowenite, californite, chrysoprase, Connemara marble, grossular, plasma, prase, prehnite, serpentine, smithsonite, verd-antique, and williamsite.
This stone is known as nephrite because in early times it was used in amulets against kidney disorders (derives its name from the Greek word for "kidney"). Both jadeite and nephrite are known as jade, so the term "nephrite jade" needs to be used to distinguish between the two.
It is fairly widespread, so much that it was used virtually everywhere by Neolithic man for polished stone weapons.
Nephrite jade was very important in ancient Oriental art, especially in China, where fine objects were fashioned from it up until the mid-18th century, when the use of jadeite jade began to be established after that period.
Beautiful nephrites in New Zealand are called Maori stone, because of their widespread use in ancient Maori art.
Although it is one of the two types types of minerals which are fully entitled to be called jade, nephrite jade is less highly prized nowadays than jadeite jade, which often has strong, attractive colors.
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 beads and pendants, and, much more rarely, cabochons and engraved pieces for setting in jewelry, as nephrite jade takes a good polish. Pale, slightly translucent and not too lustrous specimens have a greasy or waxy appearance that is characteristic of much antique Chinese jade.
Nephrite used to be cut with quartz sand; today carborundum or diamond powder is used. The main cutting centers are Canton, Peking, and Hong Kong.
The extraordinary mechanical properties and particular appearance of nephrite jade have been employed 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 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.
An imitation of nephrite jade has been produced in Japan. It consists of a paste, recrystallized to form a translucent material with felted or fascicular zones of crystals. This has a lower density than nephrite jade. It is known as imori stone or metajade.
Natural materials such as aventurine, serpentine, and the 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, for example, Indian jade, Korean jade, Transvaal jade, etc. Such names are considered an abuse of proper gemological terminology. These materials have interesting ornamental properties, but their value is lower than that of nephrite jade, and lower still than jadeite jade.
Synthetic nephrite is not produced.