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 Composition
In gemology, only two kinds of mineral are called jade. One is more formally called jadeite, like Myanmar jade. The other is called nephrite, like Fong Tian jade.
There are 7 different ways that gemstones may be crystallized (http://www.gggems.com/crystalline_system.htm). The system which Fong Tian jade belongs to is called the monoclinic system. Its specific weight is 2.96 - 3.04 and it has a hardness of 6 - 6.5. The refractive index is 1.604 - 1.631 and the birefringence index is 0.021 - 0.027. Such features result from the presence of two components, a mineral solid solution form of tremolite (Ca2Mg5Si8O22(OH)2) and actinolite (Ca2Fe5Si8O22(OH)2), making Fong Tian jade closer to tremolite in terms of the composition.
Fong Tian jade composition is often of fibers or grains, appearing dark green, emerald, yellow green or light yellow. It can be glassy and medium transparent or not. Under the microscope, it is composed of tremolite of slender fibers or fine hair-like structures, among which chromite, garnet, chlorite and magnetite are present. These form black patches or stripes. The nephrites and serpentines are both green in color, the former contains a higher quantity of SiO2 and CaO while the latter contains more MgO. Besides that, nephrites are clearer, harder and heavier than serpentines and not magnetic. The raw stone of Fong Tian jade mostly appears dark green to yellow green, semi- or non-transparent, with sophisticated structures and schistosity. Often you can see black dots or lines inside the stone.
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Mineral Distribution