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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.
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
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).
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.
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:
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.