广西大化“水草花”软玉的宝石学特征

含丰富"水草花"形态包裹体的软玉是广西大化软玉的一个独特品种,通过常规宝石学测试以及偏光显微镜、电子探针、红外光谱仪、拉曼光谱仪、X射线粉末衍射仪等仪器测试,对广西大化"水草花"软玉的矿物组成及其内部进行测试分析。结果显示,该品种软玉的主要矿物组成为透闪石。透闪石根据晶体形态及大小分为两种:一类为纤维状变晶交织结构,颗粒粒度小且均一,质量分数大于95%;一类为片状-毛毡状变晶交织结构,颗粒粒度大,多呈团块,质量分数小于5%。广西大化软玉的"水草花"为不透明锰质氧化物,呈无定形态、粉末状和片状,由后期锰质氧化物充填进入透闪石微裂隙和颗粒间隙中形成的形态各异"水草花"状包裹体。

Gemmological Characteristic of Nephrite with Dendrite Pattern from Dahua,Guangxi Province

The nephrite with dendrite pattern from Dahua, Guangxi Province, is a special kind of nephrite jade.The nephrite with variety of dendrite pattern ("Shuicaohua") is an unique species of nephrite from Dahua, Guangxi Province.In this paper, the nephrite with variety of dendrite pattern was studied with gemmological tests, polarizing microscope, electron microprobe (EPMA), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray diffraction(XRD).The gemmological testing results showed that the refractive index of samples is between 1.59 and 1.61 by point measurement and its average is 1.60.The density is between 2.89 and 2.94 and its average is 2.91.The surface of samples have variety of dendrite pattern("Shuicaohua").By observing the mineral slices under polarizing microscope, the mineral component of the samples is tremolite.The textures of tremolite are classified in two types.One is fibrous intergrowth crystalloblastic texture, and the tremolite grains are distributed uniformaly and its content is more than 95% in general.The other is flaky intergrowth crystalloblastic texture, and the tremolite grains is distinctly larger and its content is less than 5%.According to the electron microprobe (EPMA) test, the content of MnO in white-gray tremolite (without dendrite pattern) is between 0.21% and 0.35%, and the content of MnO of dendrite pattern is between 0.94% and 3.96%.It is concluded that the dendrite pattern ("Shuicaohua") is caused by MnO.The formation of dendrite pattern ("Shuicaohua") should be probably due to fracture filled with MnO.