Jade is one of the oldest worked materials in human history and one of the most culturally loaded in the gem trade. The English word denotes two mineralogically distinct rocks — jadeite and nephrite — that were not separated until 1863, when the French chemist Alexis Damour demonstrated that the Chinese imperial "jade" of the late Qing dynasty (which is jadeite, sourced from upper Burma from about 1784) and the older Chinese cultural "jade" worked since the Neolithic (which is nephrite) are two different minerals. The trade today recognises both species under the umbrella term "jade" but requires species disclosure (jadeite or nephrite) at retail under most national codes and CIBJO Blue Book rules.

Mineralogy

Jadeite is a sodium-aluminium clinopyroxene, NaAlSi₂O₆, in the pyroxene group. It crystallises in the monoclinic system, with a Mohs hardness of 6.5 to 7.0, a specific gravity of 3.30 to 3.38 (the higher of the two species), and a refractive index of 1.652 to 1.688. Pure jadeite is white; coloured varieties take their colour from chromium (the imperial green that defines the highest tier of the market), iron (the green-yellow and apple greens, the brown and the black variants), manganese (the rare lavender to violet jadeite of the upper Burmese deposits), and copper (rare).

Nephrite is a calcium-magnesium-iron amphibole, Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂, of the actinolite-tremolite series. It is also monoclinic, with a Mohs hardness of 6.0 to 6.5, a lower specific gravity of 2.90 to 3.03, and a refractive index of 1.600 to 1.640. Nephrite's distinctive toughness — it is the toughest of the natural rocks in standard reference, exceeding even jadeite — derives from its felted, fibrous, interlocking amphibole microstructure. The colour range runs from white ("mutton-fat" of the Chinese tradition) through the spinach greens to the dark green-black variants.

Source localities

The principal jadeite source for both historical and contemporary trade is the Hpakant region of Kachin State, upper Myanmar, where the species has been mined since at least the late eighteenth century and where the world's only commercial-quality imperial-green jadeite is produced. Secondary sources include Guatemala (the source of the Olmec and Maya pre-Columbian jade tradition), Russia (Polar Urals), Kazakhstan, Japan (Itoigawa) and California; none rivals Burma in commercial quantity or quality.

Nephrite is more widely distributed. The historical Chinese sources of Hetian (Khotan) and Manass in the Tarim Basin and the Kunlun Mountains supplied the Chinese imperial nephrite tradition for several thousand years. Other major sources include Russia (Lake Baikal and East Sayan), New Zealand (the Maori pounamu tradition), British Columbia (the principal contemporary commercial source, see separate Jade BC entry), Wyoming, Australia and Taiwan. The British Columbia mines, particularly Cassiar and Polar Mines, have been the dominant supplier of nephrite to the Chinese carving market since the 1970s.

Cultural and trade history

The Chinese nephrite tradition begins around 5000 BC with the Hongshan and Liangzhu Neolithic cultures and runs continuously through the dynasties to the present, encompassing ritual cong and bi forms, archaic-revival imperial work, scholarly carving and the Republican-period Beijing and Shanghai workshops. The shift to jadeite at the imperial court is dated to the late Qianlong reign (the 1780s), with the Burmese supply opened by the Ch'ing's tribute relations. The Empress Dowager Cixi is the most-cited late Qing patron of jadeite. Pre-Columbian Maya and Olmec jade is jadeite from Guatemalan sources, and the Maori pounamu tradition is nephrite from the South Island.

Quality grading

The principal quality factors for jadeite are colour (the imperial-green standard), translucency (the "glassy" or bo li zhong grade, in which the stone passes light readily, is the highest), texture (the fineness of the grain, with the highest tier showing no visible structure under ten-power magnification), and treatment status (see below). The trade speaks of A, B, C and B+C jade, codes set out in the GIA, GIT and Chinese national standards: A is untreated, B is bleached and polymer-impregnated, C is dye-impregnated, and B+C is both. Only A-jade is acceptable in the high-end traditional Chinese trade, and the price differential between A and B+C is conventionally 100 to 1 or greater for fine material.

The principal quality factors for nephrite are colour saturation, structural homogeneity (absence of black inclusions or structural banding), and origin (Hetian white nephrite of the historical Chinese imperial trade commands a substantial premium over Russian or Canadian material of equivalent visual appearance).

Treatment and detection

The bleaching-and-polymer-impregnation treatment of jadeite, which entered the Hong Kong market in the late 1980s and is the principal treatment concern in the modern trade, is detected by infrared (FTIR) spectroscopy showing the polymer C-H stretching bands, by Raman spectroscopy, and by long-wave ultraviolet fluorescence (treated stones often show a milky-blue glow absent in untreated material). The 1990s emergence of widely available B-jade caused a major repricing of the jadeite market and led to the establishment of the GIT, NGTC and HRD jadeite-grading certificates that are now standard for high-value pieces. Dyeing is detected by colour-concentration patterns along fractures and by spectroscopic methods. Nephrite is generally less treated, but dyeing and oil impregnation occur in the lower tiers.

Trade structure

The contemporary jadeite market runs through three principal channels: the Yangon and Mandalay rough-jade emporiums in Myanmar (now operating under sanctions; see Jade BC, JADE Act 2008), the Hong Kong cut-stone and finished-jewellery wholesale market, and the mainland Chinese retail market. The retail premium for fine imperial-green jadeite has, since 2000, repeatedly outpaced equivalent-grade ruby and emerald, and exceptional pieces (the Hutton-Mdivani Necklace, the Doris Duke jadeite, the Cartier-mounted Burmese jadeite cabochon ropes) regularly achieve eight-figure auction prices. The nephrite market is structurally smaller, dominated by the Chinese carving trade for Hetian and Russian-Siberian material with British Columbian supply playing the volume role.