Nephrite is one of the two distinct minerals commonly known as jade. While nephrite doesn’t match the variety or the fine green “imperial jade” colors found in jadeite, it does occur in attractive colors, including green, and is even more durable as a gem material for jewelry and carved art objects.
China is the principal popular consumer market for both jadeite and nephrite. Elsewhere, the market is dominated by collectors. Although jadeite is the more highly coveted jade variety, nephrite is more abundant. Thus, green nephrite that approximates jadeite’s color is prized as an alternative. White nephrite or “mutton fat” jade remains a traditional favorite and the most popular nephrite variety on the Chinese market. Siberian nephrite, with a dark “spinach green” color and black graphite inclusions, is considered the most valuable green nephrite variety for Western consumers.
Nephrite and jadeite are both considered jade, but they’re distinct minerals with different properties and natural formation processes. Nephrite belongs to the tremolite-actinolite mineral series. Stones closer to tremolite have higher magnesium content and lighter colors, such as the celebrated, creamy white “mutton fat” jade. Higher iron content gives nephrites closer to actinolite darker colors, like green. Combinations of these elements as well as traces of other elements and inclusions can create yellowish, grey, and brown varieties. Skilled gem carvers can utilize a brownish skin or surface on green stones to create a cameo-like effect.
Generally, green nephrites are less bright and intense than green jadeites. With few exceptions, nephrite shades usually appear dark and somber.
Although less hard than jadeite, nephrite’s dense, fibrous structure makes it tougher for carving purposes. With hardness of 6 to 6.5, nephrites do have some susceptibility to scratching, so protective jewelry settings are recommended, especially for ring use. However, for practical purposes, both nephrite and jadeite make excellent jewelry stones.
Both actinolite and tremolite, the end members of the mineral series that includes nephrite, are considered asbestos. However, nephrite is not considered to be an asbestiform mineral, despite having a fibrous structure. Wearing nephrite jewelry and handling rough or finished pieces pose no health risks. Nevertheless, lapidaries should take precautions when cutting nephrites. Working with nephrites might pose a risk of silicosis and it is recommended wearing a respirator, wet-grinding, and wet-mopping the work area.
Large commercial quantities of good quality nephrite occur in B.C., extending from the northern provincial boundary, southeastward to the lower region of the Fraser River. The nephrite occurs as small to very large boulders, some weighing more than 15 tons (one specimen was estimated to weigh 80 tons). The best quality (in terms of colour, and solidity) comes from the central to northern part of the province. Known sources of nephrite yielding commercial quantities are being mined in the Atlin Lake, McDame, Dease Lake, Wheaton Creek and Turnagain River, Mt. Ogden- Fort St. James areas. In 1970 a 23 ton boulder from the Mt. Ogden area, was exhibited outside the B.C. pavilion at Expo 70 in Osaka Japan. Nephrite from the Bridge River- Fraser River area is highly variable, even within the same boulder. Vivid hues are rare, with predominant colours being dark green, grayish-green, olive, and yellow-green. Some material is so dark that it appears black, but true black has not been found.