摘要：
Grayish green nephrite is named for a kind of nephrite belonging to green nephrite type, but with appearance similar to gray nephrite. Although their appearance is similar, the price of grayish green nephrite is much higher than that of gray nephrite. Thus a phenomenon appears that some dealers tell their consumers green nephrite while selling gray nephrite. In addition, some jade materials with such appearance appear in some unearthed jade artifacts, but their types can not be accurately identified. This makes it particularly important to quickly and accurately identify grayish green nephrite and gray nephrite. In this study, representative grayish green nephrite and gray nephrite samples were investigated using ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy and electron microprobe analysis, and all the characteristics were yielded. By comparing the features between them, it can be found that there is no significant difference in the UV-Vis reflection spectra of both types of samples. However, the differences in the infrared spectra of them are recognizable. In order to explore more effective identification features, the reflection and transmission methods were used to obtain infrared spectra. The infrared spectra of both types of samples were generally the same, with the following distinguishable differences. The peak or shoulder around 1 050 and 1 018 cm-1 and the broad shoulder near 411 cm-1 occur in the reflection spectra of grayish green nephrite which do not appear in those of gray nephrite. The shoulder around 453 cm-1 and the peak near 401 cm-1 exhibit in the transmission spectra of the gray which do not exist in those of the grayish green. The above findings can be used as spectral characteristics to identify grayish green nephrite and gray nephrite. The intensity of the OH stretching vibration bands at 3 674, 3 661 and 3 643 cm-1 after Beer-Lambert Law transformation of the infrared transmission spectra and the Mg and Fe2+ content in the M1 and M3 sites are well correlated. The Mg (M1+M3) # (Mg/ (Mg+Fe2+) in the M1 and M3 sites) ratio calculated by the relationship between the above two can be used to distinguish between grayish green nephrite and gray nephrite using their infrared transmission spectra. Mg (M1+M3) # ratio in grayish green nephrite (0.871～0.892) is smaller than that of gray nephrite (0.927～0.949). Moreover, the result of electron microprobe analysis showed that there are some differences in chemical composition between them. Mg content in grayish green nephrite (4.45～4.53) is less than that of gray nephrite (4.66～4.78), and Fe2+ content in the grayish green (0.28～0.49) is larger than that of the gray (0.10～0.23). However, Mg and Fe2+ content between them are not much different from each other, suggesting that the difference in infrared spectra may be related to the physicochemical conditions during crystallization besides having a certain correlation with the composition (the genetic types of grayish green nephrite and gray nephrite are ultrabasic rock type and dolomitic marble type, respectively). The above infrared spectrum identification features not only have important gemological significance for identification of grayish green nephrite and green nephrite, but also have potential application value for discriminating origin and analyzing occurrence of some ancient jades with the similar appearance to the studied nephrites.%青碧为碧玉系列中外观类似青玉的称呼.二者虽外观相似, 但青碧价格高很多, 故市场上出现了以青玉充青碧售卖的现象.此外, 一些出土玉文物中也出现了这类外观的玉石材质, 但无法准确判别其类型.这使得快速准确鉴别二者有十分重要的意义.采用紫外-可见光谱、傅里叶变换红外光谱和电子探针分析方法, 给出了青碧和青玉样品的谱学特征和矿物的化学组成等特征, 并进行了对比分析.二者在紫外-可见反射光谱上没有明显差异, 然而, 二者的红外光谱特征存在可识别的差异.为了探讨出更有效的鉴别特征, 采用了反射和透射两种方法来获取红外光谱.二者的红外光谱总体上一致, 有以下可区分差异特征:青碧的红外反射光谱中出现了青玉光谱中未出现的1 050和1 018 cm-1附近吸收峰、肩峰及411 cm-1附近宽肩峰;青玉的红外透射光谱中出现了青碧光谱中未出现的453 cm-1附近肩峰和401 cm-1附近吸收峰.以上可作为快速鉴别青碧和青玉的谱学特征标志.红外透射光谱经朗伯-比尔定律 (A=log (1/T)) 转换后, 在3 674, 3 661和3 643 cm-1附近处的OH伸缩振动谱带的强度与M1, M3位的Mg及Fe2+含量有很好的相关性.利用以上二者关系计算的Mg (M1+M3) # (在M1和M3位的Mg/ (Mg+Fe2+)) 值可用于鉴别青碧和青玉.青碧的Mg (M1+M3) #值为0.871～0.892, 小于青玉0.927～0.949.另外, 电子探针分析结果显示青碧和青玉的化学成分存在一定差异:青碧Mg含量 (a.p.f.u) 为4.45～4.53, 比青玉的4.66～4.78小;青碧Fe2+含量为0.28～0.49, 大于青玉的0.10～0.23.但部分青碧和青玉间的Mg和Fe2+含量差异不大, 说明红外光谱差异除了与成分有一定的关联性外, 可能还与结晶时的物理化学条件有关 (青碧和青玉的成因类型分别为超基性岩型和白云质大理岩型).以上红外光谱识别特征不仅在鉴别青碧和青玉上具有重要的宝石学意义, 还在古代玉制品源区的判别、产状分析等方面具有潜在的应用价值.
