一类绿松石仿制品的宝石学特征研究

The Gemological Characteristics of One Kind Turquoise Imitation

绿松石的仿制品由来已久,早期主要以染色压制碳酸盐为主,后期陆续出现天然矿物的绿松石仿制品,如染色磷铝石、染色玉髓以及染色菱镁矿等,这些仿制品普遍不具有天然绿松石的颜色和结构特征,物理和光学性质与天然绿松石也有较大差异。选取市场上新出现的一类绿松石仿制品为研究对象,采用常规宝石学测试方法、红外吸收光谱及X射线粉晶衍射重点对其矿物组成、宝石学性质以及结构特征进行了研究。研究结果表明:该类绿松石仿制品表面可见角砾状构造,铁线浮于表面,分布形态单一,蓝色样品上可见明显的深蓝色颗粒,白色样品上见少量黑色点状物质,为典型的压制处理特征,蓝色绿松石仿制品则经染色压制处理。此类绿松石仿制品折射率在1.54~1.58,较天然绿松石低并具明显的蓝白色紫外荧光,可作为鉴别其与天然绿松石差异的重要证据。X射线粉晶衍射说明该类绿松石仿制品主要由顽火辉石与石英组成。红外吸收光谱显示该类绿松石仿制品的吸收谱峰主要表现为顽火辉石的典型吸收光谱,在1 088和799 cm^(-1)附近的吸收峰则与石英中的Si—O和Si—O—Si伸缩振动有关;2 947和2 882 cm^(-1)附近的吸收峰与外来的有机树脂中CH_2的伸缩振动有关,1 736和1 510 cm^(-1)附近的吸收峰,则由C=O伸缩振动和CH_2的弯曲振动所致。

It has been a long time that the imitations of turquoise appear in gem market.Pressed dyed carbonate in the early stage and dyed variscite,chalcedony as well as magnesite appeared in succession.These kinds of materials do not have the color and characteristics of natural turquoise.Their physical and optical properties are quite different from natural turquoise.One kind of turquoise imitation newly appears in market is selected to be studied in this paper.The conventional gemological method,infrared absorption spectroscopy and X-ray diffraction were employed to study its mineral compositions,gemological properties and structural characteristics.The results show that：the brecciated structure can be observed and the distribution of the iron wire is very simple on the surface of the sample.Deep blue granules arc visible on the surface of blue samples and a few black spots can be observed on the surface of white ones,which are typical indication of pressing process.The blue imitations of turquoise has been stained and pressed.The index of this kind of turquoise imitation range from 1.54 to 1.58,which is lower than that of natural turquoise and it show bluish white fluorescence,which can be used as important evidence to distinguish it with natural turquoise.The data of X-ray diffraction shows the sample mainly consists of enstatite and quartz.The results of infrared absorption spectroscopy show that the absorption spectra of this kind of turquoise imitation is in accordance with the typical absorption peaks of enstatite：the absorption peaks which locates near 1 088 and 799 cm^-1 are associated with Si—O,Si—O—Si stretching vibration in quartz;the absorption peaks near 2 947 and 2 882 cm^-1 is related with stretching vibration of CH2 of exotic organic resin;the absorption peaks near 1 736 and 1 510 cm^-1 are resulted from the bending and stretching vibration of C=O and CH2.