Jade
875 Words
Bill Gallagher
ok to reproduce not for profit in entirety with credit
Jade is a very generic term, encompassing several different types of stone, although the rocks most associated with the word Jade are two usually green and semi-translucent metamorphic formations high in silica. Distinguishing between the various kinds of stone which comprise Jade is quite literally an aspect of the science of Mineralogy. The two kinds of metamorphic rock the term "Jade" generally describes are Nephrite -- Ca(Mg,Fe)3(SiO3)4 -- which posesses a microcrystaline interlocking fibrous matrix; and Jadeite -- NaAl(SiO3)2 -- which is a member of the alkaline pyroxene group of minerals, and is comprised of a microcrystaline interlocking crystal, versus fibrous, matrix. Most of the time very little distinction is made between nephrite and jadeite, but there are purists in every field of endeavor and the field pertaining to Jade certainly has some too. Nephrite is the more common form, and has a specific gravity of 2.9 to 3.1. Jadeite has a specific gravity of 3.3, and this allows determination between the two rocks with decent accuracy. Both types, nephrite and jadeite, have splintery fractures, and are categorized within the monoclinic crystal system. There are other types of material called jade by different people at different times, such as the massive Green Grossularite Garnet from Buffelsfontein Transvaal, which has been called African or Transvaal Jade, but labels like these are incorrect descriptions, and are usually an attempt to beef up a stones value commercially, because Jade is well liked in the lapidary world, and the better Jades can be very very expensive.
Jade has a lot of historic significance, being not only used for ornamentation since ancient times, but for many tools and vessels as well. The stone is nearly unparalleled in its toughness, though its hardness is sometimes as low as a seven on a scale of ten, making it relatively easy to work. Under most conditions it also polishes well, and has certain tactile characteristics of smoothness which also endear it to its users and admirers. The Chinese and other oriental peoples have always had a reverence, even a religious attitude toward Jade, believing it is imbued with the five cardinal virtues of charity, modesty, courage, justice, and wisdom. The oriental peoples also hold certain colors of jade, other than green, in very high regard, though in the Orient, and indeed elsewhere, the very greenest and glowy jade products are valued in the thousands of dollars per carat.
Cutting and polishing of jade is an art in itself among lapidary endeavors, and many people who work with a certain type of nephrite or jadeite guard their polishing processes closely. Because there is a fairly high degree of variety among the various types of the rock, there are necessarily varieties in the way it is worked. Diamond tooling is almost always good for all kinds of stone, though there are polishing processes for jade incorporating silicon carbide, silica powders, cerium oxides, and many more. After wrestling with jade for some years any lapidary artist will definitely do what it takes to maintain a polishing process that works, because that is a fairly rare and valuable circumstance. It many times pays to get a little heat going in the final stages, letting the polishing pad dry out somewhat. This puts a high burnish on some of the more ornery jade types, but too much heat can cause burning, and then its time to start all the grinding steps over, or just pitch the thing and start with a new blank. With jade, the saying: Practice Makes Perfect, reaches new heights of applicability. Jade cabochons, beads, and carvings ranging in size from small, to megalithic, are always in demand.
Nephrite in quantity is found in in China, Turkestan, Siberia, British Columbia, New Zealand, Alaska, Wyoming, New Zealand, and in small quantities almost everywhere else. Jadeite is found in Burma, Southern China (Yunnan), Tibet, Mexico, and South America. In Coulterville, California, Mariposa County, are, or were, some fee dig sites for Nephrite: The Jade King Mine 2 miles south of town, and the nearby Ming, Green Dragon, and Four Jacks claims. At Covelo California, in Mendocino County, nephrite and Jadeite can be found on top of Leech Lake Mountin, which is about 15 miles NE of town. Also in the north fork of the Eel River, where the road north to Mina crosses the river, at Dos Rios to southwest, and at Dryden ranch 6 miles east, reached by Mendocino pass road, fee. At Eureka in Humboldt County nephrite and jadeite pebbles can be found on the beaches from Patrick Point State Park 28 miles north on US 101, to Dry Lagoon, 8.5 miles farther north. Also in the Trinity River 40 miles east and in other nearby areas. In British Columbia nephrite can be found as pebbles and boulders at Agassiz in the bars of the Fraser River. Throughout the entire Northwestern area of United States and south western Canada is good hunting for nephrite and jadeite. In Lander, Wyoming, (Fremont County) are some of the best sources for nephrite, in colors ranging from black to light green and everything in between. Many claims are evident in that area and most of the creeks and rivers will provide good hunting for the rockhound.
Kraus and Slawson, Gems and Gem Materials, Mcgraw-Hill 1947.
Simon and Schusters Guide To Gems
Simon and Schusters Guide To Rocks and Minerals
The Gem Hunters Guide, Russel P. MacFall
Wikipedia, Jade
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