俄罗斯绿泥石玉的矿物学特征研究

Study on Mineralogical Characteristics of Chlorite Jade from Russia

  • 摘要: 采用折射仪、紫外荧光灯、X射线衍射分析以及扫描电子显微分析, 对一种近来出现在市场上的玉石新品种、来自俄罗斯的绿泥石玉—“天使之玉 (seraphinite) ”—的宝石学特征、微观结构及其矿物学特征进行了研究。结果表明, 该绿泥石玉呈深绿色、微透明—不透明集合体, 具鳞片变晶结构, 裂隙少, 质地均匀, 在紫外荧光灯下不发荧光, 摩氏硬度为2.5, 折射率为1.58, 密度为2.60g/cm3。X射线衍射分析结果表明, 该绿泥石玉的物相为绿泥石。扫描电子显微分析结果表明, 绿泥石晶体发育良好, 可见不同排列方向上的绿泥石晶体集合体呈交叉分布。能谱结果表明, 该绿泥石晶体的化学组成w(MgO) 为35.4%, w(Al2O3) 为14.8%, w(SiO2) 为32.6%, w(FeO) 为4.2%, w(H2O) 为13.0%。该绿泥石玉基本由斜绿泥石组成, 斜绿泥石的晶体化学式为:Mg6(Fe0.7Mg3.8Al1.5)(Si6.2Al1.8)O20(OH)16;晶体呈定向排列, 颗粒较大的片状晶体产生波状弯曲现象。这些结构特征是造成该绿泥石玉具有丝绢光泽的可能原因。

     

    Abstract: The gemmological characteristics, microstructure and mineralogical characteristics of a newkind of chlorite jade—“seraphinite”— from Russia, which is recently presented in the gem markets, are studied by using refractometer, ultraviolet fluorescence lamp, X-ray diffraction (XRD) and scanning electron microscope (SEM). The results showthat the chlorite jade is in dark green, semi-translucent to opaque, and lepidoblastic texture, with hardness of 2.5, refractive index 1.58 and density 2.60 g/cm3. It has homogeneous texture and less fissures, and no fluorescence under ultraviolet fluorescence lamp. XRD analysis shows that the mineral composition of the chlorite jade is mainly chlorite. SEM results showthat the chlorite exhibits well-developed crystal. It also can be seen that the chlorite aggregates in different directions showa crossed distribution. The chemical analysis suggests that the chlorite contains w(MgO) 35.4%, w(Al2O3) 14.8%, w(SiO2) 32.6 %, w(FeO) 4.2% and w(H2O) 13.0%. The jade is composed of almost clinochlore, with a chemical formula Mg6(Fe0.7Mg3.8Al1.5) (Si6.2Al1.8) O20(OH) 16. The chlorite crystal is in oriented distribution. In addition, the large particles of the schistose crystals exhibit wave-shaped bending. Both the microstructure and mineralogical characteristics are probably responsible for silky luster of the chlorite jade.

     

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