Gemmological Characteristics of Agate from Madagascar
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摘要: 采用常规宝石学测试方法以及偏光显微镜、X射线粉末衍射仪、电子探针、傅里叶红外光谱仪等仪器测试手段对产于马达加斯加的一种具有特殊白色花纹的玛瑙的宝石学特征进行了系统研究。结果表明，马达加斯加玛瑙中不同颜色部位的化学成分均为SiO2，主要矿物组成为石英，石英多呈纤维束状大致平行排列或者以小的角度彼此相交，而垂直于条带的石英纤维，则呈韵律状变化。X射线粉末衍射测试2θ＝68°处的衍射峰得到，马达加斯加玛瑙中石英的结晶度指数为1.33，远低于理想的石英晶体，推测马达加斯加玛瑙是由富硅熔浆在低温下快速冷凝凝结而成。Abstract: The conventional gemmological methods,polarizing microscope,X-ray powder diffraction spectrometer,electron microprobe,infrared spectrometer,and cathodoluminescence were used in this paper for studying the agate sample from Madagascar with special white patterns.The results show that the chemical composition of the part with different colours in the agate sample from Madagascar is SiO2,and the main mineral component is quartz.The quartz fiber parallels each other or intersects in small angle.On the basis of analysis of X-ray powder diffraction peaks at 68°,the crystallinity index of agate sample from Madagascar is 1.33,which is much lower than that of ideal quartz crystal(crystallinity index is 10).It is presumed that agate sample from Madagascar was formed by a fast siliciaous magmatic melting at the low temperature.
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Keywords:
- agate from Madagascar /
- gemmlogical characteristic /
- XRD /
- crystallinity index
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