四川龙溪软玉的宝石矿物学特征

Gemmological and Mineralogical Characteristics of Nephrite from Longxi, Sichuang Province

  • 摘要: 基于四川龙溪软玉资源的综合开发利用现状及存在的问题,采用X射线粉末衍射仪、电子探针、傅里叶变换红外光谱仪、激光拉曼光谱仪、偏光显微镜等分析测试仪器,就该地区软玉的化学成分、矿物组成、结构、振动光谱等特征进行测试分析。结果表明,龙溪软玉的主要矿物为透闪石,次要矿物为方解石、白云石、滑石及磷灰石等;整体为纤维变晶结构,局部呈交代残余结构。类比其它矿区相似矿床产出的软玉,龙溪软玉的化学成分以相对贫Fe富Mg为特征;在中红外波数范围内,由νas(Si-O-Si)反对称伸缩振动导致的一组红外吸收谱带位于1 000~1 200 cm-1范围内,由νas(Si-O)反对称伸缩振动和νs(Si-O)对称伸缩振动导致的红外吸收谱带分别位于990、955 cm-1和926 cm-1处,600 cm-1范围下的吸收谱带为δ(Si-O)弯曲振动及M-O伸缩振动所致。近红外波数范围内,由OH(MgMgMg)、OH(MgMgFe2+)、OH(MgMgFe3+)倍频振动导致的红外吸收峰分别位于7 181、7 151、7 133 cm-1附近。构造应力作用易导致该地区部分软玉样品中微裂纹发育,并且不同程度影响龙溪软玉的玉质。

     

    Abstract: Based on the current situation and existing problems of the comprehensive development and utilization of nephrite resources in Longxi, Sichuan Province, X-Ray diffraction, electron probe, Fourier transform infrared spectrometer, laser Raman spectrometer, polarizing microscope and other analytical testing equipments were adopted. The chemical composition, mineral components, structure, vibration spectrum and other characteristics of nephrite in the area were studied. The results showed that the main mineral of nephrite from Longxi is tremolite, and the minor minerals are calcite, dolomite, talc and apatite. Nephrite has a fibrous metamorphic structure as a whole, and a partial metasomatic residual structure. Similar to nephrite produced from similar deposits in other mining areas, the chemical compositions of nephrite from Longxi are characterized by relatively poor Fe and rich Mg. In the mid-infrared wavenumber range, a set of infrared absorption bands caused by νas (Si-O-Si) antisymmetric stretching vibration is in the range of 1 000-1 200 cm-1. The infrared absorption bands caused by νas (Si-O) antisymmetric stretching vibration and νs (Si-O) symmetric stretching vibration are located at 990, 955 cm-1 and 926 cm-1, respectively. The absorption band below 600 cm-1 is caused by δ (Si-O) bending vibration and M-O stretching and vibration. In the near-infrared wavenumber range, the infrared absorption peaks caused by OH (MgMgMg), OH (MgMgFe2+) and OH (MgMgFe3+) frequency-doubled vibrations are located near 7 181, 7 151 cm-1, and 7 133 cm-1, respectively. Tectonic stress can easily lead to the development of microcracks in some samples of nephrite in this area, and affect the quality of nephrite from Longxi to varying degrees.

     

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