jade, hyvä kirkas vihreä sävy
|Mitat :||4,1 x 3,9 x 2,1mm|
|Väri :||kirkas vihreä|
|Ominaista :||lähes pyöreä|
|Erikoista :||imperial jade, kirkas vihreä väri|
|Found only in a remote area of northern Burma (Myanmar), jadeite is one of the world's most expensive gemstones. Jadeite jewelry is highly prized especially in the Orient and exceptional pieces rival the prices of top diamond and emerald jewelry and sell for millions of dollars. Even rough or cut stones may fetch huge sums. Although the name jade refers to two separate mineral species, jadeite and nephrite, the materials have no relation to one another except that of appearance. Both are very tough and are used in a wide range of carvings but jadeite is much more rare and expensive. Jade is mainly fashioned as carvings, beads, bangles, or cabochons for rings, earrings or brooches.|
|Color Key:||Pure white thru pink, brown, red, orange, yellow, mauve, violet, blue, and black, to an extensive range of green and mottled green and white.|
|Refractive Index:||1.654 - 1.667|
|Ocurrence:||Northern Myanmar. Non commercial discoveries of Jadeite have also been reported in China; Russia (in the Polar Urals); Niigata, Japan; San Benito County, California, USA, and Guatemala.|
|As a result of some forty years of controlled archeological research in China, it is now known that the ancient Chinese had been working green materials they call “yu” for over 7000 years. Jadeite, often known as Chinese jade is found only in Myanmar but the material did not enter China until the eighteenth century and therefore was not the true jade which was so cleverly carved by the Chinese craftsman of ancient dynasties. Their jade certainly included the mineral nephrite but not jadeite.|
Jadeite consists of an aggregate of interlocking crystals of the monoclinic system. It is one of the pyroxene group of minerals and is allied to spodumene, diopside and enstatite. Jadeite is a sodium aluminum silicate, NaAl(SIO3)2), but a varying percentage of the diopside CaMg(SIO3)2), and/or kosmochlor (ureyite) NaCr(SIO3)2) molecules are often present. Jadeite has a hardness of 7 (equal to quartz) on the hardness scale. The SG lies between 3.30 and 3.36 and the refractive index ranges between 1.654 to 1.667.
While Nephrite is only green or dark green, jadeite is found in most colors from pure white thru pink, brown, red, orange, yellow, mauve, violet, blue, and black, to an extensive range of green and mottled green and white colors. A jadeite containing a considerable amount of the oxides of iron is known as chloromelanite; it is dark green to black in color. The SG of chloromelanite is somewhat higher and may reach 3.5. The mauve color in jadeite has been attributed to the presence of manganese and the duller greens to iron. Another Burmese gem, Mawsitsit, is an attractive green rock with black spots, composed from at least six different minerals as main constituents including jadeite.
The most highly prized color of jadeite caused by chromium, is a rich emerald green of great translucency. To give some idea of the value of jadeite, the Mdivani necklace which contains 27 beads (15.4 to 19.2 mm in diameter), sold for US$3.88 million at the October 1994 Christie’s Hong Kong auction. The record price for a single piece of jadeite jewelry was set at the November 1997 Christie’s Hong Kong sale: Lot 1843, the “Doubly Fortunate” necklace of 27 approximately 15 mm jadeite beads which sold for US$9.3 million. Indeed, out of the top ten most expensive jewels sold worldwide by Christie’s in 1999, five out of ten were jadeite. These auctions clearly show that jadeite is among the most valuable of all gemstones.
The only important source for jadeite is upper Myanmar where is found in dykes of metamorphosed rock of the Uru valley a tributary of the Chindwin river. Tawmaw, Mainwaw, Pangmaw, and Namshamaw are the chief dykes; the primary deposit at Tawmaw outcrops for a distance of about 6 km. The tough mineral is difficult to mine and the Burmese formerly used fire to break up the deposits but drilling and blasting are now used to mine the material. Alluvial jadeite is also mined from the Uru and other rivers in the Myitkyina district. The boulders are generally covered by a brownish skin due to weathering and as in the case of nephrite, this brownish overlay may be used to create a two tone effect.
Much of the rock and the boulders were traditionally marketed through the Chinese province of Yunnan and as a result the material was often known as Chinese jade. More recently, the material has been marketed in Thailand and directly in Rangoon. The yearly Burmese gem and jade auction is an important source of income for the government of Myanmar and the event attracts a large community of foreign buyers. Hong Kong Chinese are the main players for this material. The blocks are typically “mawed” before sale - that is part of the skin is removed and the underlying material is polished to expose the inner color of the material. However, as the material is rarely uniform throughout, there is always a great deal of speculation as to, how the piece will turn out. Since it is impossible to see through the rough boulders, good luck is probably much more useful than experience.
Non commercial discoveries of Jadeite have also been reported in China; Russia (in the Polar Urals); Niigata, Japan; San Benito County, California, USA, and Guatemala.
Jadeite is often bleached or dyed to produce a more desirable color. The process involves two stages, first the removal of brown iron staining with hydrochloric acid and secondly, the impregnation of the treated jadeite with dyes and polymers like optigon and by paraffin wax which has long been used to enhance surface polish.. As well as removing the iron staining, the immersion in acids also opens up the minute cracks between the grains and these may be become more visible under magnification. Indeed the concentrations of color in the small cracks is a good way to determine if a piece has been dyed and a jade or chrome filter or UV fluorescence may also be used to highlight the concentrations of dye in the cracks. Plastic or resin impregnated jadeite has a lower SG and will float in methylene iodide. A hot thermal probe will also melt the plastic impregnation and give off an acrid smell.
In 1984, General Electric announced the synthesis of synthetic jadeite producing greens and lavender colors with textures resembling the natural material in many respects. The material was detectable with a spectroscope as the 437nm line was not present in the synthetic material. A similar process has also been patented more recently in Japan. In view of the high cost of the production, synthetic has never been produced on a commercial scale.