一种长英黝帘石玉的岩石矿物学研究

采用X射线粉晶衍射、电子探针、化学分析法和傅立叶变换红外光谱等方法,对近来在北京珠宝市场上出现的一种粉白相间的玉石新品种进行了测试,全面分析了这种玉石的结构和成分,并根据硅酸盐体系的物质平衡原理,利用相混合计算(PMC)方法,估算了玉石中主要矿物的含量。结果表明,这种玉石中黝帘石含量占51.9%,钠长石占33.3%,石英14.4%,并含有少量的褐帘石、单斜辉石等矿物。样品中粉红色矿物的红外光谱最强峰位于1110～900cm-1范围内,为快速、方便地鉴定此种玉石提供了参考依据。

Petrology and mineralogy of a new kind of felsic zoisite jade

In order to determine the petrological and mineralogical characteristics of a new kind of pink jade that appeared in Beijing jewelry market recently, the authors used X-ray diffraction(XRD), electron-probe microanalysis (EPMA) , whole rock chemical analysis and Fourier transform infrared (FTIR) spectroscopy to investigate the structure and composition of the pebble sample of this new kind of pink jade. On the basis of the mass balance principle, the proportions of the jade were estimated by means of the phase mixing calculation (PMC). The result shows that the fresh surface of this kind of jade is pink, whereas the weathered surface is yellowish gray. As for gemmological characteristics, this kind of jade is translucent to opaque and has glassy luster, with the relative density being 2.93. With the variation of the proportion of minerals, the refraction indices vary between 1.56 and 1.70. The minerals of the jade are mainly zoisite, albite and quartz, with small amounts of allanite and clinopyroxenes. Results of EPMA and whole rock chemical analysis with the adoption of PMC show that this kind of jade contains 51.9% zoisite, 33.30% albite, 14.4% quartz, 0.6% allanite and 0.1% clinopyroxenes. XRD data have given the same conclusion. The strongest infrared absorption bands of the pink mineral appear in the range of 1 110～900 cm~(-1), similar to the peak value of standard zoisite, indicating that the main mineral of this jade is zoisite, and hence this new jade is a kind of felsic zoisite jade. In comparison with chemical composition of other colors of zoisites, the trace element Mn is very high, suggesting that the pink color of this kind of jade is caused by Mn. These results provide valuable reference for the rapid and accurate deter-mination of the jade.