| Jade is the gem name for
mineral aggregates composed of either or both of two different minerals, Jadeite
and Nephrite. Jadeite is a sodium-rich aluminous pyroxene; nephrite is a
fine-grained, calcium-rich, magnesium, iron, aluminous amphibole. All jade is composed of
fine-grained, highly intergrown, interlocking ("matted" or "felted"
texture, like asbestos or felt) crystals of one or both of these minerals. Though neither
mineral is very hard (6-7), jade is one of the toughest gem minerals known because of the
intergrown nature of the individual crystals.
Most jade on the market is composed of nephrite; jadeite jade is quite rare and in its
emerald-green, translucent form is referred to as Imperial
Jade or "gem jade". A small amount of Cr in jadeite accounts for the
color of imperial jade. Other color-based names for jadeite jade are Yunan Jade,
for a uniquely appearing dark green, semitranslucent jade, Apple Jade for apple
(yellowish green) green jade, and Moss-in-Snow for white jade with vivid green spots and streaks.
Nephrite and jadeite jade ranges in color from
a somewhat greasy-appearing, white ("mutton fat jade") to dark and light shades
of green, gray, blue-green,
lavender, yellow, orange, brown,
reddish-brown, and black. An important dark green variety of nephrite is sometimes known
as "spinach jade". The chromophore in all nephrite jades is usually Fe. Nephrite
jade is usually opaque to translucent in thinner pieces.
The name jade has been, and continues to be,
applied to a variety of materials that superficially or closely resemble jade but are not
composed of either jadeite or nephrite. F.T.C. regulations in this country deem such usage
unlawful, yet the practice persists, either through ignorance or otherwise. Some of the
problem can undoubtedly be traced to cultural and historical differences in word usage. In
China, for example, the word jade has traditionally been applied not only to nephrite and
jadeite jade, but to green serpentine and soapstone (talc) whose appearance closely
resemble true jade. Common misnomers and the materials they represent are:
"Korean" Jade for serpentine or gem serpentine (bowenite), "Indian"
Jade for aventurine, "Mexican Jade" for green-dyed calcite, "Transvaal
Jade" for green hydrogrossular garnet, "Amazon or Colorado Jade" for
amazonite (blue-green or green) feldspar and "Oregon or Swiss Jade" for green
chalcedony.
Properties
- Crystal System: Monoclinic
- Habit: Fibrous crystals, densely matted together. Usually
found as water-washed pebbles or boulders. Rare
botryoidal habit known.
- Hardness: Nephrite: 6 - 6.5 Jadeite: 6.5
- 7
- Toughness: Extremely tough
- Cleavage:2 directions; not evident in jade
- Fracture: Splintery
- Specific Gravity: Nephrite: 2.90 -
3.02 Jadeite: 3.3 - 3.5
- R.I.: Nephrite about 1.62 Jadeite
about 1.66
- Color: See above
- U.V. Fluorescence: Lighter colored jadeites have a weak
whitish color in long U.V. light; nephrite doesn't fluoresce
- Phenomena: Chatoyance, yielding fine
cat's eyes in rare pieces (Korea, Alaska, Russia).
Distinguishing Properties
- Difficult to impossible to distinguish nephrite jade from jadeite
jade by visual inspection. Specific gravity determination is the most reliable of
simple I.D. methods for distinguishing the two.
- Great variety of materials offered as imitations, e.g. talc
(soapstone), serpentine, amazonite, dyed chalcedony, and others. All can have colors
remarkably similar to jade, but properties above, particularly S.G., can be used to
distinguish.
- Dyed jade can be most easily distinguished from undyed jade by
examination with a Chelsea filter; undyed jadeite will not show the red color of dyed
jadeite or nephrite when looked at through the filter.
Sources
Jadeite is a mineral that is restricted in
occurrence to certain metamorphic rocks that have undergone metamorphism at high pressures
but relatively low temperatures. Jadeite jade is found exclusively as nodular or
lens-shaped masses in serpentinite. Nephrite jade, which is also a product of metamorphism
(and fluid infiltration), does not apparently require the very special P-T conditions of
jadeite and is much more widespread. It is also found in association with serpentinite in
all known localities. Because of its extreme toughness in contrast to the weaker material
it forms in (serpentine), jade is nearly always found as weathered boulders and cobbles in
stream deposits or glacial sediment. Historically and presently important jade producing
localities are:
- Upper
Myanmar (Burma), near Tawmaw and Hpakon
- Sole source of Imperial Jade; since mid 1700's
- Highly prized by late dynastic Chinese Emperors.
- Also the source of Yunan jade (nephrite).
- Turkestan (central Asia between Iran and Siberia)
- Earliest known source of nephrite
- Used by early Chinese for carving
- Southern Fraser River drainage,
British Columbia
- Fine nephrite, supports large industry
- Some nephrite
as veins within serpentinite.
- Wyoming, near Lander; since 1936
- Nephrite boulders, some very large (house-size), in glacial
deposits that cover the chaparral and desert country around Lander.
- Some lovely green jade; also "golden jade", a golden
brown variety.
- New Zealand, South Island
- Fine green nephrite originally carved by natives into religious
objects and weapons
- Alaska, in Kobuk River Watershed at Jade Mountain
- Some cats' eye nephrite reported
- Fine greens and whites
- Others: Poland (white nephrite); Taiwan; Monterey Co., California
(poor quality jadeite); Guatemala (green jadeite); Japan; U.S.S.R. (near Lake Baikal,
green nephrite).
Shaping and Treatment
- Has long been used as carving material in
Asia and China, where it is
fashioned into religious and ornamental objects. As a jewelry stone, it is either carved
(intaglios), polished en cabochon, or fashioned into beads, bracelets or rings.
- The quality of the jade is taken into account when fashioning. In
Hong Kong, the world center for jadeite cutting, dealers earmark the best pieces (free of
white or black streaks, fractures) for cabochons, followed in descending order for lesser
material by bracelets, beads, carvings and disks ("doughnuts").
- Dying white jade to a mauve or green color (particularly to an
imperial jade color) is the most common treatment. Can be detected with a loupe by careful
inspection; the color will be seen to be distributed along grain boundaries rather than
throughout the stone. Obtaining a written guarantee from the seller is the best way to
protect yourself from dyed material.
- Several green (dyed or otherwise) materials are used as imitations
(see above).
Pricing and
valuation
A difficult subject best left to a jade
expert. Color, transparency and the uniformity of both of these are of principle
importance when judging the material. Design, craftsmanship and antiquity play equally
important roles when evaluating carved objects.
The following generalities apply:
- Color is of principle importance. True imperial jade is the most
highly prized; the best "imperial green" color has been likened to the color of
fine emerald. Matched cabochons of average size can be worth 10's of 1000's of dollars.
Next in value are somewhat lighter shades, then lavender, dark apple green,
"forest" or "spinach", light apple green, and dirty or spotty green.
The most highly prized colors are those that are pure, intense, and uniform.
- The following additional factors are important, particularly for
jade cabs., bracelets, or rings:
- Color Uniformity: should be free of blotchiness.
- Translucency: should be semitransparent in natural light.
- Clarity: should be inclusion-free when illuminated from the back
by a strong light. Dark or light veins, spots, or blotches detract from value.
- Brightness: should exhibit a lustrous brilliance or
"glow".
- Cabochon prices vary by weight and size according to color. Ovals
are in greatest demand. The purported largest jade cabochon to be
sold at auction, a gem weighing 121.16 ct., sold for $1,722,000 in
May, 2000.
- Objects are priced according to artistic merit and the way in
which the colors in a piece enhance the beauty of the carving.
- Jewelry that is well match with respect to color commands a 20-30%
premium in price.
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