Nephrite Jade — The Trade Name for Amphibole-Aggregate Jade
Nephrite Jade — The Trade Name for Amphibole-Aggregate Jade
A near-synonym for nephrite, used in the trade to mark the species against its more famous cousin jadeite
Nephrite jade is, in current trade usage, a near-synonym for nephrite, with the additional word jade serving the practical function of identifying the material to a wider audience for whom the bare mineralogical name might mean less. The expression is essentially redundant from a mineralogical standpoint — nephrite is by definition a jade, and one of only two species that legitimately bear the name — but it is in widespread use in retail descriptions, auction catalogues, and laboratory reports, where it serves to mark the species clearly against its more famous and more expensive cousin jadeite. The substantive content of nephrite jade is identical to nephrite, and the technical and historical material in this entry mirrors the longer reference article on the species.
Why two species are called jade
The term jade was adopted by Spanish conquistadors in the sixteenth century from the indigenous use of the green stone in Mesoamerica — piedra de la ijada, the loin stone, in reference to its supposed efficacy in treating kidney complaints. For most of the history of European contact with Asian and Mesoamerican jade, the term was applied to whichever green ornamental stone was at hand, and the mineralogical distinction between the two underlying species was not made. The chemical and crystallographic separation of the two materials is a nineteenth-century scientific development. The French mineralogist Alexis Damour established in 1863 that the green stone of the Chinese imperial tradition encompassed two distinct species, which he named nephrite (from the Greek for kidney, retaining the historical sense) and jadeite (a back-formation from jade itself). Both names have been in continuous use since.
The legal and gemmological position is now well settled. Nephrite is a calcium-magnesium-iron amphibole aggregate of tremolite-actinolite. Jadeite is a sodium-aluminium pyroxene of the clinopyroxene group. Each is independently a jade in the legal and trade sense, and the two together exhaust the legitimate scope of the term.
Mineralogy in brief
Nephrite jade is monoclinic in its individual amphibole crystals, but the gem material is a microcrystalline aggregate with an interlocking fibrous habit. Hardness 6 to 6.5 on the Mohs scale, specific gravity 2.90 to 3.03, refractive index spot reading approximately 1.62. Cleavage is good in the underlying amphibole crystals but is masked by the fibrous aggregate, and the species is therefore exceptionally tough rather than fragile in cleavage. Colour ranges from white through cream and pale celadon to a wide spectrum of greens, with rare yellow, brown, and black material; iron content is the principal control on colour.
Sources and the principal varieties
The principal contemporary sources are Russian Siberia, Chinese Hetian, Canadian British Columbia, and New Zealand. American Wyoming has produced significant historic material. The reference article on nephrite covers each source in more detail.
Within the species, several named varieties are in regular trade use. Mutton-fat (yang zhi yu) is the white to creamy-white Hetian material that the Chinese imperial tradition prized above all others. Hetian is the broader Chinese-trade name for material from the Khotan region of the Tarim Basin. Pounamu is the Māori name for New Zealand nephrite, with subdivisions including kahurangi (pale celadon to translucent green), kawakawa (deep olive green), inanga (pale grey-green), and tangiwai (technically bowenite serpentine, distinct from true nephrite but historically grouped with pounamu in Māori usage). Greenstone is the older English-language name for New Zealand nephrite, now displaced in formal usage by pounamu but still common in the trade.
Identification
Distinguishing nephrite from jadeite is routine. Specific gravity is the cleanest single indicator: jadeite is denser at 3.30 to 3.36, nephrite lighter at 2.90 to 3.03. Refractive index follows the same pattern (jadeite higher at around 1.66; nephrite around 1.62). Infrared spectroscopy is definitive. Polish quality differs visually — jadeite typically takes a more lustrous polish than nephrite — but the visual distinction is unreliable in commercial-grade material.
Distinguishing nephrite from non-jade simulants is the more practical commercial issue. Serpentine (including bowenite), hydrogrossular garnet, californite (massive vesuvianite), and aventurine quartz are all sometimes traded as jade, and the use of the name nephrite jade rather than the bare jade is in part a defensive disclosure against this slippage. CIBJO, AGTA, and the major laboratory disclosure standards require that the material be identified specifically, and the use of jade alone, without species qualification, is increasingly understood as inadequate disclosure.
Treatment
The standard for fine nephrite is no treatment. Lower-grade material is occasionally dyed, and dye is detectable through long-wave ultraviolet examination, immersion in refractive-index liquids, and infrared spectroscopy. Polymer impregnation, which is a major issue in jadeite (the B and B+C grades of the Chinese trade nomenclature), is less common in nephrite, but the same disclosure framework applies.
In the trade
Use of the term nephrite jade rather than nephrite alone is a matter of audience and disclosure. Auction catalogues for Chinese works of art, museum object descriptions, and laboratory reports typically use nephrite simpliciter, on the assumption that the reader understands the species to be a jade. Retail descriptions, gem encyclopaedias, and consumer-facing material frequently add the word jade as a clarifier, particularly where the surrounding context might lead a buyer to assume that any green ornamental stone bearing the name jade is jadeite. Both usages are accepted, and the underlying material and its properties are identical regardless of which name is used.