Canadian Rockhound: The Jades

As you all know, the name Jade includes both nephrite and jadeite. Taken separately, nephrite is a silicate of calcium and magnesium (with some iron in the ferrous state) and belongs to the amphibole group. Jadeite, the "companion" mineral, is a silicate of sodium and aluminum belonging to a group of rock-forming minerals known as pyroxenes. Both are inosilicates characterized (as the name suggests) by sinews or chains of silica tetrahedra. These may be simple oxygen-linked strings or complex double chains latterly bonded to various types of cations, that is, positively charged atoms, that produce differing mineral species such as diopside, enstatite, jadeite, spodumene and the like. The pyroxenes have simple, single chains whilst double-chain structures are characteristic of the amphiboles, such as nephrite, hornblende, tremolite, actinolite, etc.

As rough, minerals from the two groups can be distinguished by cleavage: 56° for the amphiboles (tremolite) and 90° for the pyroxenes (diopside). Too, it should be noted that pyroxenes are anhydrous, whilst amphiboles contain water and will give off water vapour or steam when heated in a closed test-tube. Also of interest is the fact that the amphiboles tend to be fibrous, acicular or elongated in habit. Both jadeite and nephrite are monoclinic. To my knowledge, no individual crystals of nephrite itself occur, but I have seen tiny, drusy jadeite crystals in a boulder cavity or "vug" from Burma.

Dean Field
At the time this issue went to press, the Canadian Rockhound was informed of the passing of Dean S.M. Field. Dean was the founder of the Canadian Gemmological Association. Dean grew up at Advocate Harbour, a tiny N.S. village near Parrsboro. Photograph © 2000 Willow Wight.

Nephrite Jade

The traditional jade of China was, of course, Nephrite. It was worked in that country as early as the Late Neolithic period (ca. 3000-1500 B.C.). Apparently, all the nephrite rough was imported from sources outside China, for even in modern times there seems to be no substantiated Chinese deposits. It is believed that the Chinese sources for nephrite were located, in olden times, in East Turkistan, from which boulders were transported for many centuries over most difficult transcontinental routes to their final destination in China. During the past century, however, much of the rough destined for China came from New Zealand, Siberia and Canada.

The best green nephrite I have ever examined was exceptionally hard and compact and took almost a mirror finish when polished with diamond in the modern manner. It came from British Columbia during the late 1950's and early 1960's, and is still being mined there at several localities. Its hardness (about 6.5) is very close to that of jadeite and the colour is a deep apple green. It was, for the most part, completely free from concentrations of chromite and other impurities. A Dube carving of a large angel fish cut from one of the pieces of that nephrite is here and available for hands-on inspection.

The fact that nephrite from other localities does not generally accept an even polish is, in my belief, due to (1) the presence of other minerals – associated or as inclusions – and/or (2) variations in the felting of the crystals that comprise the variety of jade we know as nephrite. Some sections have been shown to be more densely matted than others, hence take a higher polish than do adjoining less-tightly felted areas.

Additionally, it may be said that the matted structure of nephrite jade makes it one of the toughest but certainly not the hardest mineral known. It was the recognition of this property that probably induced the world's ancient peoples to utilize it for the making of weapons, tools, bowls, vases and, as civilization advanced, carved images of flora and fauna of both secular and religious significance.

The late B.W. Anderson stated that some of the jade from Taiwan showed a distinct chatoyancy and there was a tendency to market stones cut from this green material as "nephrite" cat's-eyes, but this was discouraged by leading gemmologists. Their judgment was based on the fact that "although the composition and properties of these stones are akin to nephrite, their structure consists of strictly parallel fibres to which the chatoyancy is due, whereas in nephrite the fibres are in random orientation as a tangled mass in typical jade fashion." He went on to say that, "Analysis has shown that the most accurate description of these cat's-eyes would be 'tremolite cat's-eyes'!" Several tremolite and one actinolite cat's-eye are here and on display.

Jadeite Jade

Jadeite is somewhat less tough but slightly harder than nephrite. It has a fine granular structure of interlocking crystals that may vary slightly in hardness. This gives rise to a subtly dimpled surface when the material is cut and polished. In late years, however, the use of diamond in the polishing process has made the dimpling much less apparent. It has also resulted in a higher polish, making the age of the piece more readily recognized as modern or re-finished.

Jadeite was introduced to Chinese artisans only about the middle of the 18th century, during the reign of the emperor Ch'ien-lung (1736-1795). It is said that the Chinese knew of the jadeite of Burma since the 13th century of the Christian era; but some five hundred years elapsed before any jadeite jade reached China and was worked on anything like a large scale. This was due not so much to transportation difficulties as it was to a long-lasting "cold war" and political conditions, generally. The Chinese and Burmese were definitely not good trading partners. Even when it was brought to China, Burma jadeite took almost a century to become accepted as a valuable stone; and it was probably due to the old empress dowager, Tz'u Hsi, who loved its bright, vivid colours, that it finally reached pre-eminence as the Imperial Stone or most precious thing, in China. It is generally believed that no art objects were created in China from jadeite much prior to that time. Indeed, it is fairly safe to date intricately carved vases and the like fashioned in jadeite jade to the various periods after about 1780 A.D.

Jadeite, with a hardness of 7 on the Mohs' scale of relative hardness, occurs in white, grey, pale blue, pale lavender, yellow, mutton-fat cream, orange, brown, burnt-sienna red, black and, of course, green. The greens are most favoured in the Western world and vary greatly in saturation and hue, from the palest of greens to a deep translucent emerald hue. The Chinese also favour an even darker translucent green colour, but this has the tendency to appear blackish in artificial light. The rare fancy colours are also gaining world-wide attention for their rarity and innate beauty, especially when they are set next to the brighter green shades.

Although green jadeite and emerald both owe their colour to chromium, green jadeite does not show red under the Chelsea filter, nor does it do so under either LW or SW UV light. With the spectroscope, however, green jadeite shows several bands in the violet, the strongest being at 437 nm. It is intense enough to be discerned by reflected light and by transmitted light if the material is not too opaque or too dark in colour to transmit well. Naturally green jadeite also shows three chromium lines somewhat resembling steps or louvres in the red, at about 630, 660 and 690 nm. In contrast, dyed green jadeite may show one broad band extending from about 630 to 670 nm; but above this is a light zone from about 670 to the end of the visible spectrum. In the "natural green" spectrum just described, there is nothing but darkness above the 690 nm band. Note however, that the band at 437 nm is present in both the natural and dyed examples.

Lavender jadeite is also frequently dyed. Anything but a pale shade is immediately suspect. Koivula (1982) reports that dyed lavender jade shows orange under LW UV light. This is also true, l have found, of the lavender-dyed alabaster simulant on display here to-day. The two large lavender jade cabochons are inert.

Most jadeite regardless of colour will remain suspended or very slowly sink in methylene iodide (di-iodomethane) that has a density of about 3.32-3.33 at normal room temperature. The mean R.I. of jadeite is 1.66 (alpha 1.654; gamma 1.667). This mean R.I. can be determined quite readily by the distant vision method. Strangely enough, if the stone is loose and has a flat back, the alpha and gamma values can be read off and the birefringence of 0.013 determined even though the material is actually a multi-crystal aggregate.

Whilst deposits of gem quality nephrite are widespread throughout the world, there is only one source of any importance for the varieties of jadeite used in modern jewellery, and for carvings and art objects. That source is located at My-it-ky-ina in the Shan mountain district of Upper Burma, about 100 to 125 km west of the town of Mogaung, which is the sorting and storage centre. No jadeite is found anywhere around Mogaung itself, and about the only way to get to it is by a rather ramshackle plane. Although My-it-ky-ina is the most northerly train depot, only the occasional train makes it that far north, and that sporadically. My-it-ky-ina was one of the main Japanese air bases in Burma during the occupation of the Second World War. The town is located on a raised plateau surrounded by a flat fertile plain through which a branch of the Irrawaddy flows.

All jade from the in-place deposits, as well as boulders from the rivers northwest of the village, are transported by truck and jeep to Mogaung, where they are examined, tested, tried, graded and marked, and stored for shipment to the south. If the mines are producing, helicopter service could probably be used now, but for countless years, the crudest (and probably the cruellest) means of transportation were used. The instability of the politico-economical situation in Burma has halted much of the jade and ruby mining in Burma, and we can only speculate on what is in store for future developments of these quality-unique deposits.

References

Anderson, B.W. (1980) Gem Testing, 9th ed.
Arem, J. (1983) Rocks & Minerals.
Field, D.S.M. (1974) Jade the Mineral, Canadian Antiques Collector, July/August.
Fitzgerald, F.C. (1969) History of China. American Heritage.
Koivula, J.l. (1982) Some Observations of the Treatment of Lavender Jadeite, Gems & Gemology, 28(1), p. 32-35.
Liddicoat, R.T (1981) Handbook of Gem Identification, GIA.
Meen, V.B. (1963) Gem Hunting in Burma.
Webster, R. and Anderson, B.W. (1983) Gems, 4th ed (rev.).

This article may not be copied, distributed or reprinted in any form without permission from Mrs. Willow Wight, editor of the Canadian Gemmologist. To contact the editor, please use the e-mail address provided. If you are unable to contact the editor, please contact the Canadian Rockhound. Authorized reprints must acknowledge the author, original source and the Canadian Rockhound.

The preceding article was a short address by the late Dean S.M. Field at the CGA Gem Conference, given on October 20, 1990 at George Brown College, Toronto.