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. Siberian nephrite, with a dark “spinach green” color and black graphite inclusions, is considered the most valuable green nephrite variety.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Is a Variety of||Jade|
|Alternate Common Names||Jade|
|Crystallography||Monoclinic. Masses of fibrous crystals, densely packed and very tough.|
|Colors||Creamy beige (mutton fat jade) when rich in Mg. Green colors, due to Fe. Brown (oxidized Fe); sometimes a surface skin is dark brown. Also yellowish, grayish brown, yellow-green, black.|
|Luster||Vitreous to greasy; dull.|
|Fracture||Splintery. Very tough.|
|Specific Gravity||2.90-3.02; usually 2.95.|
|Spectral||Doublet at 6890, two vague bands at 4980 and 4600; sharp line at 5090.|
|Transparency||Opaque to translucent.|
|Phenomena||Chatoyancy, but see "Comments" below.|
|Pleochroism||Strong dichroism, masked due to the fibrous nature of the material.|
|Optics||a = 1.600-1.627; γ = 1.614-1.641. Biaxial (-). Usually, refractometer shows a shadow edge at about 1.62.|
|Etymology||From the Greek word nephros, meaning “kidney.” The rounded, kidney-like shape of nephrite boulders and pebbles likely led people to regard these stones as cures for kidney ailments, via sympathetic magic. See jadeite.|
|Occurrence||Contact and metamorphosed iron and magnesium-rich rocks. Nephrite is most frequently encountered in the form of rolled boulders.|
|Inclusions||Chromite and graphite “black dots;” parallel tremolite crystals create whitish stripes known as “water lines” in the Chinese trade.|
For thousands of years, Chinese artisans made incredible jewelry and works of art from a stone they called yu. In the mid 18th century, fei-ts’ui, an intense green-colored stone, entered China from Burma (Myanmar). Both materials soon became known as one mineral in the West, jade, due to their similar external appearance. In 1863, the mineralogist Alexis Damour distinguished jade as two distinct minerals. In effect, this reaffirmed the distinction the Chinese made originally. What the Chinese called yu, scientists identified as nephrite. Fei-ts’ui was identified as jadeite.
The term “jade” still enjoys widespread use both in the gem trade and in everyday parlance. However, gemologists should distinguish between nephrite jade and jadeite jade.
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 more wearable as jewelry and tougher for carving purposes.
Cat’s Eye Gems
Taiwan has produced chatoyant nephrites. However, there is some dispute over what to call this material. Although these stones also belong to the tremolite-actinolite mineral series, their structure differs from nephrite’s. Parallel fiber arrangements cause their chatoyancy. These cat’s eyes come closer in composition to tremolite and, more commonly, actinolite. (Ferroactinolite content = 10%).
The cat’s eyes colors include greenish to honey yellow, dark green, dark brown, and black. Their properties are:
- Optics: a = 1.613-1.616; β = 1.626; γ =1.632-1.637.
- Birefringence: 0.016.
- Specific Gravity: 3.01-3.05.
Nephrites have not been synthesized. However, many natural gems and synthetic materials can simulate their external appearance. Possible natural imitations (or candidates for misidentification) include amazonite, chrysoprase, pectolite, and serpentine gemstones such as bowenite and verd antique.
Many misleading names for gemstones include the term “jade.” These may be offered for sale as nephrites. See the jadeite gem listing as well as our List of False or Misleading Gemstone Names for more information.
The principal sources of gem-quality nephrite are Canada, China, and Russia.
- Fraser River, British Columbia, Canada: dark-colored nephrite.
- Russia (Lake Baikal): dark, spinach green color with abundant graphitic black inclusions or spots, very distinctive fine color.
- China (Sinkiang Province): generally light in color.
- Fengtien, Taiwan: spinach green to pea green, in seams in rock; despite abundance of material on market in former years, large pieces are very scarce. Also cat’s eyes.
Other notable sources include:
- United States: Alaska (green colors, in very large masses, sometimes fibrous and chatoyant); California (alluvial material, various green shades, in boulders up to 1,000 pounds); Wisconsin: (gray-green color, not too attractive); Lander, Wyoming (boulders mottled green with white, very distinctive material).
- Cowell, South Australia: material similar to New Zealand; large amounts potentially available.
- New Zealand: Maori Greenstone, in situ and in boulders, usually dark green to black.
- Poland: creamy white to gray-green, with green patches (near Jordansmuhl).
- Germany; Mexico; Mashaba district, Zimbabwe.
Alluvial boulders of several tons are not uncommon in certain localities.
Chinese artists have long mastered the art of carving this material. Some carvings use only one side of a boulder, leaving the rough shape as a background. Immense nephrite brush pots and statues grace many museums around the world. Of special note is the M. M. Vetleson jade collection that occupies an entire room at the Smithsonian Institution.
Large fine pieces are always carved, for example, the sculpture Thunder, by Donald Hord, in Wyoming jade (145 pounds).
- American Museum of Natural History (New York): displays a huge block of nephrite from Poland, weighing 4,718 pounds.
- Smithsonian Institution (Washington, DC): displays a boulder of several hundred pounds, sliced open, with a thin slab backlit to show the color.
Untreated nephrite jewelry requires no special care. You can use mechanical cleaning systems such as steam and ultrasonic. However, use a soft brush, mild detergent, and warm water for treated material or if you’re uncertain of treatment. Gemology labs can confirm what, if any, treatments your jewelry has received. See our Gemstone Jewelry Cleaning Guide for additional care recommendations.