俄罗斯“绿龙晶”的成分和结构特征研究

Study on the Composition and Structure Characteristics of“Lvlongjing”from Russia

随着近几年文玩市场的兴起,"绿龙晶"成为人们喜爱的一类新兴的宝玉石品种。目前对于"绿龙晶"的主要矿物组成的认识仍存分歧。采用常规宝石学仪器测试、电子探针、红外吸收光谱和X射线粉晶衍射测试方法对产自俄罗斯的"绿龙晶"玉的基本性质、化学成分、红外吸收光谱及矿物组成特征等进行了较为详细的研究分析。结果显示:俄罗斯"绿龙晶"玉主要为深绿至灰绿色,表面具有特殊的放射状花纹及典型的丝绢光泽,折射率约为1.57,密度为2.61g·cm-3。"绿龙晶"中SiO2的含量为36.177%~36.651%,MgO含量为36.439%~36.730%,Al2O3含量为11.961%~12.318%,FeO含量为2.304%~2.853%,具富镁贫铁特点。样品中Al/(Al+Mg+Fe)为0.185 3~0.215 9,推测其为镁铁质岩蚀变成因。样品中的Si=3.10~3.40,Fe^(2+)/R^(2+)=0~0.024 8,属叶绿泥石类型。"绿龙晶"的红外吸收光谱为特征的绿泥石振动谱峰,高频区3 673cm^(-1)附近的吸收峰为OH伸缩振动所致,1 400cm^(-1)附近吸收峰属OH弯曲频率,1 000cm^(-1)附近的三个吸收峰由Si—O伸缩振动致,400~600cm^(-1)之间的吸收谱带属于Si—O弯曲振动。其中中频区1 000cm^(-1)附近分裂的三个吸收峰1 051,1 006和968cm^(-1)可作为鉴定其为叶绿泥石的关键证据。X射线粉晶衍射分析结果与化学成分及红外吸收光谱分析结果一致,显示"绿龙晶"中的主要组成矿物为叶绿泥石,非斜绿泥石。

As the rise of heritage players market in recent years,＂Lvlongjing＂jade from Russia has become a favorite new gem varietiy.At present,there are disputes over the main mineral composition of the＂Lvlongjing＂.In this paper,a more detailed research and analysis of the fundamental nature,chemical composition,infrared absorption spectrum characteristics and mineral composition of the＂Lvlongjing＂from Russia has been made via conventional gemological test,electronic probe,infrared absorption spectroscopy and X-ray powder diffraction method.The result shows that the＂Lvlongjing＂from Russia is mainly dark green to gray-green in color,with a special surface radial pattern and the typical silky luster.Its refractive index is about 1.57,a density about 2.61g·cm-3.The SiO2 content of the＂Lvlongjing＂is about 36.177%~36.651%,MgO content about 36.439%~36.730%,Al2O3 content about 11.961% ~12.318%,FeO content about 2.304% ~2.853%,showing a magnesium-rich and iron-poor feature.The Al/（Al＋Mg＋Fe）in samples studied is 0.185 3~0.215 9,suggesting the causes of altered mafic rocks.The Si=3.10~3.40,Fe2＋/R2＋=0~0.024 8,showing it is a Pennine type.The infrared absorption spectrum is characterized by chlorite vibration peaks.The absorption peak near 3 673cm-1 in high frequency region is caused by the OH stretching vibration.The absorption peaks near 1 400cm-1 belong to OH bending frequency.Three peaks near 1 000cm-1 are caused by the Si—O stretching vibration.The absorption bands between 400 to 600cm-1 belong Si—O bending vibration.Three split absorption peaks near 1 000cm-1 in the intermediate frequency region,including 1 051,1 006 and 968cm-1 can be identified as key evidence of the Pennines.The analysis results of X-ray powder diffraction are consistent with the chemical composition and infrared absorption spectrometry analysis,showing the major component mineral of＂Lvlongjing＂from Russia is Pennine,instead of Clinochlore.