“荆山玉”的宝石矿物学特征

Gemmological and Mineralogical Characteristic of Quartz Jade from Jingshan

  • 摘要: “荆山玉”因产于湖北保康县古荆山一带而得名,是近年来新开发的一个石英质玉品种,其外观颜色艳丽,质地坚硬,雕刻性能良好。利用偏光显微镜、X射线粉末衍射、化学分析、红外光谱等测试方法对“荆山玉”的化学成分、矿物组成、结构构造等岩石矿物学特征进行研究。结果表明,“荆山玉”的主要矿物是石英,含少量的赤铁矿、针铁矿、磷灰石、方解石、白云石、绢云母等次要矿物;其主要化学成分为SiO2,含少量Na2O、MgO、Al2O3、P2O5、K2O、CaO、Fe2O3、FeO等,据TFe/Ti和Al-Fe-Mn比值及成因判别图解,表明组成“荆山玉”的硅质晶体属于热水沉积成因。外观上,“荆山玉”的产出状态呈角砾状和块状居多,颜色以黄色和红色为主,镜下观察具有隐晶质结构、隐晶-微晶结构、镶嵌结构及角砾结构;黄色和红色色调与铁质有关,分别赋存于针铁矿、纤铁矿和赤铁矿等铁氧化物和氢氧化物中,因Fe的价态和量的多少而呈现色调和浓度的变化。

     

    Abstract: The quartz jade from Jingshan is named from a mountain from Baokang country, Hubei Province, which is a new type of quartz jade and characterized by bright colours, high degree of hardness, unique breccia texture and easily caved.Without large-scale advertising, the popularity and market recognition of the quartz jade from Jingshan are far less than those of Huanglong jade and nanhong agate.According to the old documents, the quartz jade from Jingshan, "Jing jade" and He's jade represent the local culture of the Jingchu area, central China.The quartz jade from Jingshan is of extremely high research and collection values.
    Methods, including polarizing microscope, X-ray powder diffraction, chemical analysis and infrared spectroscopy were used to study the chemical composition, and mineral component of the quartz jade from Jingshan.The results showed that the quartz jade from Jingshan is dominant by quartz with trace hematite, goethite, apatite, calcite, dolomite and sericite.SiO2 is the major chemical composition, with Na2O, MgO, Al2O3, P2O5, K2O, CaO, Fe2O3 and FeO.TFe/Ti and Al-Fe-Mn diagram suggest that the quartz jade from Jingshan was precipitated by hydrothermal sedimentary genesis.The quartz jade from Jingshan samples is mainly brecciaous or massive with yellow or red colours, and of being cryptocrystalline, cryptocrystalline-microcrystalline structure, mosaic or brecciaous texture under the optical microscopy.Fe element exists in iron oxides and hydroxides such as goethite, lepidocrocite and hematite, and its valence and content affect the hue and concentration of quartz jade from Jingshan.

     

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