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Jade is the gem name for mineral aggregates composed of either or both of two different minerals, Jadeite and Nephrite.

Filed under: Mineral of the day,regular postings — Gary March 23, 2007 @ 11:15 pm

jade rough_jadequartz_jade_rough

An ornamental stone, jade is applied to two different rocks that are made up of different silicate minerals. Nephrite jade consists of the calcium- and magnesium-rich amphibole mineral actinolite (aggregates of which also make up one form of asbestos). The rock called jadeitite consists almost entirely of jadeite, a sodium- and aluminium-rich pyroxene.

The English word ‘jade’ is derived from the Spanish term piedra de ijada (first recorded in 1565) or ‘loin stone’, from its reputed efficacy in curing ailments of the loins and kidneys. ‘Nephrite’ is derived from lapis nephriticus, the Latin version of the Spanish piedra de ijada.


Because both were used by Stone and Bronze Age cultures for similar purposes, and they are both about as hard as quartz, exceptionally tough, beautifully coloured and can be delicately shaped, it was not until the 19th century that a French mineralogist determined that “jade” was in fact two different materials.

During the Stone Age of many cultures, jade was used for axe heads, knives, and other weapons. As metal-working technologies became available, jade’s beauty made it valuable for ornaments and decorative objects. Jade has a Mohs hardness of between 6.5 and 7.0, so it can be worked with quartz or garnet sand, and polished with bamboo or even ground jade.

Nephrite can be found in a creamy white form (known in China as “mutton fat” jade) as well as in a variety of green colours, whereas jadeitite shows more colour variations, including dazzling blue, lavender-mauve, pink and emerald-green colours. Of the two, jadeitite is rarer, documented in less than 12 places worldwide. Translucent emerald-green jadeitite is the most prized variety, both now and historically. As “quetzal” jade, bright green jadeitite from Guatemala was treasured by Mesoamerican cultures, and as “kingfisher” jade, vivid green rocks from Burma became the preferred stone of post-1800 Chinese imperial scholars and rulers. Burma (Myanmar) and Guatemala are the principal sources of modern gem jadeitite, and Canada of modern lapidary nephrite. Nephrite jade was used mostly in pre-1800 China as well as in New Zealand, the Pacific Coast and Atlantic Coasts of North America, Neolithic Europe, and southeast Asia. In addition to Mesoamerica, jadeitite was used by Neolithic Japanese and European cultures.

Jade is the official gemstone of British Columbia, where it is found in large deposits in the Lillooet and Cassiar regions. It is also the official gemstone of the state of Alaska, found particularly in the Kobuk area. A two ton block of jade sits outside the Anchorage Visitor’s Center in downtown Anchorage, Alaska, mined from near Kobuk and donated to the city as a showpiece.

History

Prehistoric and Historic China

During Neolithic times, the key known sources of nephrite jade in China for utilitarian and ceremonial jade items were the now depleted deposits in the Ningshao area in the Yangtze River Delta (Liangzhu culture 3400–2250 BC) and in an area of the Liaoning province in Inner Mongolia (Hongshan culture 4700–2200 BC). Jade was used to create many utilitarian and ceremonial objects, ranging from indoor decorative items to jade burial suits. Jade was considered the “imperial gem”. From about the earliest Chinese dynasties until present, the jade deposits in most use were not only from the region of Khotan in the Western Chinese province of Xinjiang but also from other parts of Chian,like Lantian,Shaanxi. There, white and greenish nephrite jade is found in small quarries and as pebbles and boulders in the rivers flowing from the Kuen-Lun mountain range northward into the Takla-Makan desert area. River jade collection was concentrated in the Yarkand, the White Jade (Yurungkash) and Black Jade (Karakash) Rivers. From the Kingdom of Khotan, on the southern leg of the Silk Road, yearly tribute payments consisting of the most precious white jade were made to the Chinese Imperial court and there transformed into objets d’art by skilled artisans as jade was considered more valuable than gold or silver.

Jadeitite, with its bright emerald-green, pink, lavender, orange and brown colours was imported from Burma to China only after about 1800. The vivid green variety became known as Feicui (翡翠) or Kingfisher (feathers) Jade. It quickly replaced nephrite as the imperial variety of jade.

Prehistoric and Historic Korea

The use of jade and other greenstone was a long-term tradition in Korea (c. 850 B.C. – A.D. 668). The craft production of small comma-shaped and tubular ‘jades’ using materials such as jade, microcline, jasper, etc in southern Korea originates from the Middle Mumun Pottery Period (c. 850-550 B.C.), when such ornaments appeared in burials and pit-house floors (Bale and Ko 2006). Comma-shaped jades are found on some of the gold crowns of Silla royalty (c. A.D. 300/400-668) and sumptuous elite burials of the Korean Three Kingdoms. After the state of Silla united the Korean Peninsula in A.D. 668, the widespread popularisation of death rituals related to Buddhism resulted in the decline of the use of jade in burials as prestige mortuary goods..

Māori

Nephrite jade in New Zealand is known as pounamu in the Māori language, and is highly valued, playing an important role in Māori culture. It is considered a taonga, or treasure, and therefore protected under the Treaty of Waitangi, and the exploitation of it is restricted and closely monitored. The South Island of New Zealand is Te Wai Pounamu in Māori – “The [land of] Greenstone Water” – because that is where it was found.

Weapons and ornaments were made of it; in particular the ‘mere’ (short club), and the Hei-tiki (neck pendant). These were believed to have their own mana, handed down as valuable heirlooms, and often given as gifts to seal important agreements. With no metal tools, it was also used for a range of tools such as adzes.

In New Zealand English the normal term is “greenstone” and jewellery of it in Māori designs is widely popular with locals of all races, and with tourists – although much of the jade itself is now imported from British Columbia and elsewhere.

Mesoamerica

mesoamerica quartz_jade_roughquartz_jade_roughquartz_jade_rough

Jade was a rare and valued material in pre-Columbian Mesoamerica. The only source from which the various indigenous cultures, such as the Olmec and Maya, for example, could obtain jade was located in the Motagua River valley in Guatemala. Jade was largely an elite good, and was usually carved in a variety ways, whether serving as a medium upon which hieroglyphs were inscribed, or shaped into symbolic figurines. Generally, the material was highly symbolic, and it was often employed in the performance of ideological practices and rituals.

Today, Guatemala produces jadeite in a variety of colors, ranging from soft translucent lilac, blue, green, yellow, and black. It is also the source of new colors, including “rainbow jade” and the unique “Galactic Gold,” a black jadeite with natural incrustations of gold, silver and platinum.

Other names

Besides the terms already mentioned, jadeite and nephrite are sometimes referred to by the following:

Jadeite

Agate verdâtre, Feitsui, Jadeit, Jadeita, Natronjadeit, Yunnan Jade, Yu-stone, Sinkiang jade

Nephrite

Aotea, Axe-stone, B.C. Jade, Beilstein, Grave Jade, Kidney Stone, Lapis Nephriticus, Nephrit, Nephrita, Nephrite (of Werner), New Zealand Greenstone, New Zealand Jade, Spinach Jade, Talcum Nephriticus, Tomb Jade.

Faux Jade

Many minerals are sold as jade. Some of these are: serpentine (also bowenite), carnelian, aventurine quartz, glass, grossularite, Vesuvianite, soapstone (and other steatites such as shoushan stone) and recently, Australian chrysoprase. “Korean jade,” “Suzhou jade,” “Styrian jade,” “Canadian jade,” “Olive jade” and “New jade” are all really serpentine; “Transvaal jade” is grossularite.

In almost all dictionaries, the Chinese character ‘yù’ (玉) is translated into English as ‘jade’. However, this frequently leads to misunderstanding: Chinese, Koreans, and Westerners alike generally fail to appreciate that the cultural concept of ‘jade’ is considerably broader in China and Korea than in the West. A more accurate translation for this character on its own would be ‘precious/ornamental rock’. It is seldom, if ever, used on its own to denote ‘true’ jade in Mandarin Chinese; for example, one would normally refer to ‘ying yu’ (硬玉, ‘hard jade’) for jadeite, or ‘ruan yu’ (軟玉, ‘soft jade’) for nephrite. The Chinese names for many ornamental non-jade rocks also incorporate the character ‘yù’, and it is widely understood by native speakers that such stones are not, in fact, true precious nephrite or jadeite. Even so, for commercial reasons, the names of such stones may well still be translated into English as ‘jade’, and this practice continues to confuse the unwary.

Enhancement

Jade may be enhanced (sometimes called “stabilized”). There are three main methods, sometimes referred to as the ABC Treatment System:

  • Type A jadeite has not been treated in any way except surface waxing. This type of jadeite, carat by carat, is the most expensive gem in the world, even more so than diamond.
  • Type B treatment involves exposing a promising but stained piece of jadeite to chemical bleaches and/or acids and impregnating it with a clear polymer resin. This results in a significant improvement of transparency and colour of the material. Currently, infrared spectroscopy is the only test for the detection of polymer in jadeite.
  • Type C jade has been artificially stained or dyed. The red colour of Red jade can be enhanced with heat. The effects are somewhat uncontrollable and may result in a dull brown. In any case, translucency is usually lost.

Type A treatment is the only enhancement acceptable to professional collectors.

thanks wikipedia.org

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