Jade is the gem name for two different mineral aggregates, jadeite and nephrite. Jadeite is a sodium-rich aluminous pyroxene; nephrite is a fine-grained, calcium-rich, magnesium, iron, aluminous amphibole. All jade is composed of fine-grained, highly intergrown, interlocking ("matted" or "felted" texture, like asbestos or felt) crystals of one or both of these minerals. Though neither mineral is very hard (6-7), jade is one of the toughest gem minerals known because of the intergrown nature of the individual crystals.
The name jade has been, and continues to be, applied to a variety of materials that superficially or closely resemble jade but are not composed of either jadeite or nephrite. In the United States, F.T.C. regulations deem such usage unlawful, yet the practice persists, either through ignorance or otherwise. Some of the problem can undoubtedly be traced to cultural and historical differences in word usage. In China, for example, the word jade has traditionally been applied not only to nephrite and jadeite jade, but to green serpentine and soapstone (talc) whose appearance closely resemble true jade. Common misnomers and the materials they represent are: "Korean jade" for serpentine or gem serpentine (bowenite), "Indian jade" for aventurine, "Mexican jade" for green-dyed calcite, "Transvaal jade" for green hydrogrossular garnet, "Amazon or Colorado jade" for amazonite (blue-green or green) feldspar and "Oregon or Swiss jade" for green chalcedony.
Properties of jade :
- crystal system : monoclinic
- habit : fibrous crystals, densely matted together. Usually found as water-washed pebbles or boulders ; rare botryoidal habit known
- hardness : nephrite 6 - 6.5 ; jadeite 6.5 - 7
- toughness : extremely tough
- cleavage : 2 directions ; not evident in jade
- fracture : splintery
- specific gravity (S.G.) : nephrite 2.90 - 3.02 ; jadeite 3.3 - 3.5
- refractive index (R.I.) : nephrite : about 1.62 ; jadeite about 1.66
- U.V. fluorescence : lighter colored jadeites may have a weak whitish color in long U.V. light; nephrite doesn't fluoresce
Sources : jadeite is a mineral that is restricted in occurrence to certain metamorphic rocks that have undergone metamorphism at high pressures but relatively low temperatures. Jadeite jade is found exclusively as nodular or lens-shaped masses in serpentinite. Nephrite jade, which is also a product of metamorphism (and fluid infiltration), does not apparently require the very special P-T (pression and temperature) conditions of jadeite and is much more widespread. It is also found in association with serpentinite in all known localities. Because of its extreme toughness in contrast to the weaker material it forms in (serpentine), jade is nearly always found as weathered boulders and cobbles in stream deposits or glacial sediments.
Jadeite sources: Myanmar (near Tawmaw and Hpakon), Guatemala, USA, Switzerland, Russia, Japan.
Nephrite sources: Canada, USA, Poland, China, Russia, South Korea, Japan, Taiwan, Australia, New Zealand, Switzerland.