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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 here to 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, whic more
often has strong, attractive colors. But nephrite jadE was
very important in ancient Oriental art, especially ir China,
where fine objects were fashioned from it up unti 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 bw not very lively green. However, the color can be
dark greer to blackish, gray or blue-gray. Grayish white is
also vers common. It 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, arc
elaborate, thin-walled vases. It is also made into necklace
beads and pendants and, much more rarely, cabochonsand engraved
pieces for setting in jewelry. It takes a good polish. Pale,
slightly translucent and not too lustrous speci mens have
a greasy or waxy appearance that is character istic of much
antique Chinese jade.
Distinctive features It is distinguished
from jadeite jad• by its felted, rather than granular,
structure, as well as itlower density and different refractive
indices (althougr these are hard to establish). It is mainly
distinguished by it density, but also by its greater hardness,
from some vane ties of serpentine, which look very similar
to the more translucent type. It is also distinguished by
its density froncertain rocks containing hydrogrossular and
vesuvianite which are often translucent and very similar.
These arf known as Transvaal or Pakistan jade, depending on
theiplace of origin.
Occurrence Nephrite jade is fairly widespread,
so mucr so that it was used virtually everywhere by Neolithic
mar for polished stone weapons. The chief sources are the
Soviet Union (Turkestan, Siberia) and New Zealand. It is alsc
found in Canada, the United States, and Australia.
Value On the whole, it is of very modest
value, beinp 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 outstandinq
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/cm3) 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,
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, i.e., Indian jade, Korean jade, Transvaal
jade, respectively. 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.
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