File:Black nephrite jade (Precambrian; central Wyoming, USA) (24664298766).jpg

Black nephrite jade from the Precambrian of Wyoming, USA. (public display, University of Wyoming Geological Museum, Laramie, Wyoming, USA)

Nephrite jade (nephritite) is a crystalline-textured to felted-textured metamorphic rock principally composed of one or more amphibole minerals (tremolite to actinolite, Ca2Mg5Si8O22(OH)2 to Ca2(Mg,Fe)5Si8O22(OH)2).

Nephrite jade was discovered in Wyoming in the 1930s, resulting in a "jade rush" that lasted for several decades. Most recovered material is alluvial jade, produced by paleoerosion of jade outcrops. Eroded clasts of jade were transported downstream and subsequently buried with other poorly-sorted sediments. Some Wyoming jade has been collected from in-situ outcrops.

Stereotypical jade is green-colored. The sample shown above is black nephrite jade, which is the most commonly encountered color in the central Wyoming jade field.

From museum signage: "Jade is an ornamental stone found in many parts of the world. Jade consists of two minerals, nephrite and jadeite. Nephrite is a vareity of the amphibole mineral actinolite: Ca2(Mg,Fe)5Si8O22(OH)2. Jadeite on the other hand is a type of pyroxene and forms monoclinic crystals. Jadeite's chemical formula is Na(Al,Fe+3)Si2O6."

"The word "jade" is derived from the Spanish term piedra de ijada (first recorded in 1565), of "flank stone", because it had a reputed efficacy in curing ailments of the loins and kidneys. Nephrite gets its name from Latin "lapis nephriticus", meaning "kidney stone" because it was often worn to remedy diseases of the kidneys."

"Jade is about as hard as quartz, quite tough, beautifully colored, and can easily be shaped. Both nephrite and jadeite were used during the Stone and Bronze Age and in the ancient dynasties of China."

"Nephrite is the most common form of the two varieties, being found in a creamy white form as well as various green hues. The green color is the result of iron within the crystal lattice. When iron is not present, the mineral is colorless to cloudy white. Jadeite, on the other hand, shows more color variations, including blue, lavender, pink, and green. Jadeite is found in fewer than 12 documented productive places around the world. The translucent emerald-green jadeite is the most valued variety, both now and historically. Places like Guatemala and Burma are principal locations for jadeite. Canada is the main producer of lapidary nephrite. Jade is the official gemstone of British Columbia, where it is found in the Lillooet, Liard, and Omenica Mining Divisions. Nephrite jade was used mostly in pre-1800 China as well as New Zealand, the Atlantic and Pacific Coasts of North America, Neolithic Europe, and Southeast Asia. Jadeite was used by Neolithic Japanese and European cultures."

"Nephrite jade is found in several places in the United States, including the states of Alaska, California, Connecticut, Georgia, Nebraska, Nevada, Oregon, Pennsylvania, Washington, and Wyoming. Jadeite on the other hand is found in California, North Carolina, Oklahoma, South Dakota, and Washington."

"Wyoming is known as the Jade State. Nephrite jade was adopted as Wyoming's official gemstone on January 25, 1967. Governor Stanley K. Hathaway signed legislation introduced by the 39th legislature, which established nephrite jade as the state gemstone of Wyoming."

"Nephrite is found in a vast region that runs roughly from Lander southwest to Farson, south to teh Red Desert in Sweetwater County, east to Seminoe Dam, north to Alcova, and westward back to Lander. Colors range from black, dark green, emerald green, apple green, gray, pink, and white. Lighter colors of jade, especially apple green, are most in demand for gemstones. Because jade hunters have scoured all over south-central Wyoming for nearly six decades, apple green jade is very rare to find."

"Sources cite that 1936 is the year of jade discovery near Lander. Starting in 1936 and ending in 1945, jade hunting was done principally by Wyoming residents. During the summer of 1945, some 7,000 to 8,000 pounds of jade were collected. Wyoming jade hunter Allan Branham, who is credited as being the person who first discovered American nephrite jade, once stated that "Jade lures and lures as no other stone. It is as bad as the "gold fever", and once entangled with jade, one seldom recovers." Large boulders of nephrite have been found in Wyoming. The largest specimen ever found was a 14,000 pound boulder of low-quality black jade reportedly found in the prospect at the southern end of the Wind River Mountains. Some of the best specimens come from the area around Jeffrey City."

Age: Precambrian (probably Proterozoic)