Geology And Geophysics

Jadite Nephrite and Rhodonite



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The very name speaks of the orient, of China, and other far away places lost in the mists of time. But in fact the name jade is from Spanish "piedra de yjado" literally "kidney stone." Yet most jade today is found in North America especially British Columbia. There are actually two distinct minerals that are classified as true jade; although among the jade workers of China there are more then forty stones recognized as jade. The two minerals recognized throughout the world as jade are jadeite and nephrite two distinct minerals. Jadeite is composed of the mineral pyroxene rich in sodium and aluminum. Nephrite is composed of the mineral "tremolite" an amphibole that is rich in magnesium silicates. Both of these minerals are characterized by long thin crystals. In each case in the stone jade both of these minerals are composed of elongated crystals that have been squeezed into a tightly entangled mass of crystals like felt. Both jades are found only in metamorphic rocks, and are classified as metamorphic rocks. They are both associated with the rock "serpentine" and are found in rock formations called serpentinites. Nephrite is also found associated with dolomitized marble where some of the calcium atoms have been replaced by magnesium atoms.

In many places jade is a common rock forming material requiring a special environment. This environment is a type of tectonics defined as an "Alpino" orogeny a type of mountain building that is characterized by an extremely high tectonic pressure and a low temperature. Mountains of this type include the Alps and the mountains of the Western Americas. They are found in long narrow high chains of mountains, a Cordillera. A good example is the Coast Range found along the Pacific Coast of North America. Jade deposits are found all along this range from Alaska to Guatemala. This type of orogeny is most often caused by the collision of an island arc and a continent.

Mountains such as the Appalachians are very poor in Jade although there is evidence that before the Acadian orogeny in the Devonian jade existed but was changed to other minerals, notably albite a type of feldspar. An orogeny such as this is called a "Hercynian" type orogeny. This type of orogeny is characterized by low pressure and a high temperature. Unlike the Alpino type of orogeny the Hercynian type covers a wide belt of mountains that are not so high. This type of orogeny will destroy jade deposits left by prior orogenies. These orogenies are usually caused by the collision of two continents.

Jadeite was discovered by the Spaniards during the conquest having been used by the Aztecs and earlier civilizations before the Spaniards. The name jade is derived from this mineral, and was anglicized to jade from the original Spanish "piedra de yjado" meaning kidney stone. Nephrite on the other hand is from the Latin "lapis nephritis" which means "kidney stone."

A similar mineral closely related to jadeite is rhodonite a pyroxene mineral basically having the same structure as jadeite but its chemistry is different with manganese substituting for the sodium and aluminum. In many places it is a stand alone mineral. In other places it is a gangue mineral associated with metal ores as a gangue mineral. A great deal of rhodonite was mined in the Urals of Russia. It was used as both a gemstone and a decorative stone. Sometimes it was used for the pillars in churches. It was also used to fashion the sarcophagus of Czar Alexander II. At other times it was used in jewelry. One of its more interesting uses was as an anvil. This was also true of rhodonite that was iron stained and useless for other purposes.

To my knowledge no jade has been found on the east coast, but rhodonite has been discovered in several places. West Cummington, Mass. Is one of these localities where it is found as glacial float. It was mined in situ in the early 20th century by Anson Betts who sold it to a company who ground it up to make welding flux. The float was also picked up for many years by the Tiffany Company of New York who fabricated it into many different products. There is a display of dinnerware made from rhodonite in the American Museum of Natural History in New York.

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