“凤凰石”的宝石学特征及矿物组成

Gemmological Characteristics and Mineral Components of“Fenghuang Stone”

近几年，珠宝市场上出现了一种商业名为“凤凰石”的蓝绿色宝石，为了查明其矿物组成及宝石学特征，笔者选取了3块样品，对其进行了常规宝石学测试和偏光显微镜下观察，采用X射线粉末衍射仪和电子探针等测试分析方法，重，点对“凤凰石”样品的矿物组成进行了研究。结果表明，“凤凰石”样品为含铜矿物的花岗斑岩，为斑岩型铜矿的产物，蓝绿色、绿色部分的折射率为1．51～1．52，平均值为1．519；密度为2．59～2．64g／cm^3，平均值为2．62g／cm^3。该样品的主要矿物组成为长石、绢云母、石英、蓝铜矿和孔雀石，其中蓝铜矿和孔雀石多呈细网脉状、浸染状分布于裂隙和矿物颗粒间。蓝铜矿中CuO的质量分数在67％左右，而孔雀石中CuO的质量分数约为70％，样品颜色主要由Cu^2＋致色。

A new kind of gem product has appeared in the jewelry market recently, which is called ＂Fenghuang Stone＂. In order to study the mineralogical and gemmological characteris- tics of the stones, the authors collected some samples from the market and did a series of tests and analyses. The samples were tested by using conventional gemmological methods, polarizing microscope, XRD and EPMA. Firstly, physical properties of the samples have been observed. The samples are blue and green. The green-blue, green and blue mineral exists between mineral grains or fissures in the form of infection and alternates with distribution between both of them. The samples are vitreous luster from being slightly transparent to opaque. The refractive index is between 1.51 and 1.52 by point measurement and its average is 1. 519. The density is between 2.59 and 2.64 g/cm3 and its average is 2.62 g/cm3. The surface of samples can not be carved by knife and ultraviolet fluorescence is inert. By observing the mineral slices under polarizing microscope, 70% of the minerals are found to be feldspar and sericite, and minor minerals are quartz, azurite, malachite, with content of 10%-20%, 10% and 3%-5% respectively. With obvious porphyritic structure,the particle sizes of feldspar and quartz are significantly different,which take up about 10%. X-ray power diffraction is used to further pies. It is found that the characteristic spectra found in both green and blue parts of samples. blue parts of samples contain potash feldspar, analyze the main mineral component of sam- of the potash feldspar, quartz and azurite are It can he concluded that both the green and quartz and azurite. According to the electron microprobe test, the content of CuO in the green part is basi- cally the same as that in the natural malachite. In the meantime,the content of CuO in the blue part is closely similiar to the content of azurite. Thus, the green part is malachite and the blue part isazurite. The content of CuOis 67% in azurite and 70% in malachite. As a re- suh, it is concluded that the colour of sample is caused by Cu2.＋.