jade, nephrite, USA, California, gems

Diamonds are said to be forever, but there are very few gemstone materials about which there has developed throughout the ages such a curious lore as there has about jade. In California, this lore has attracted statewide attention, principally because deposits containing the jade minerals, jadeite and nephrite, occur at several places throughout the state and because gem or lapidary quality jade has been recovered in substantial amounts from several of these localities. Many dense, fine-grained, green-colored rocks have mistakenly been called jade; but, from a gemological point of view, jade is a name given to the massive, gem-quality varieties of the two rock-forming minerals nephrite and jadeite. Nephrite is an amphibole, a silicate of calcium and magnesium that usually contains a small amount of iron. Jadeite, on the other hand, is a pyroxene and is a silicate of sodium and aluminum; usually, however, it contains variable amounts of two other pyroxene minerals, diopside (silicate of calcium and magnesium) and acmite (silicate of sodium and iron), which, when present in sufficient amounts, produce a dark green variety of jade called chloromelanite. It is true that nephrite and jadeite resemble each other very closely, but they can be distinguished by their different physical and chemical properties. Not only is jadeite harder than nephrite but it has a higher specific gravity. In general, the specific gravity of jadeite is 3.32 and that of nephrite is 2.98. Both of these minerals have a wide range of colors and color shades. Jade ranges in color from pure white, through every possible shade of green to amethyst, mauve, violet and light blue, yellow, orange and diverse tints of brown, red, and black. Because the colors in nephrite and jadeite usually are distributed unevenly, descriptive terms such as mutton fat, spinach green, and onion green have been employed to describe jade. Successful use of jadeite or nephrite as gem quality jade depends upon several important properties, such as desirable color, color pattern, and a certain degree of translucency. Because of this, the amount of jadeite and nephrite that is of gem quality is rather small in comparison to the amounts of these materials that are of mineralogical significance only. The occurrences of nephrite and jadeite, especially nephrite, are comparatively widespread and common in California. Most deposits of these interesting gemstone materials have been found only in or adjacent to bodies of serpentine, an association that seems to be characteristic of nephrite and jadeite occurrences throughout the world. Exceptions to this, however, are the unusual occurrences of nephrite associated with magnetite, epidote, chlorite and garnet in irregular contact metamorphic zones between granitic rocks and dolomitic limestone, near Victorville in San Bernardino County and in the western part of the Eagle Mountains in Riverside County. Many of the occurrences of nephrite and jadeite in California are well known to individuals and groups of amateur mineralogists but the several reports that follow, which have been prepared and published by the Division of Mines and Geology, describe in detail a few of the best known and most significant occurrences of nephrite and jadeite in California.