新疆、青海、俄罗斯糖白玉的宝石学特征对比分析

为了查明新疆、青海、俄罗斯三地所产糖白玉的结构、成分和成因差异,在观察原料外观特征的基础上,采用常规宝石学方法、偏光显微镜、X射线粉末衍射仪和电子探针研究新疆、青海、俄罗斯糖白玉样品,从结构类型、矿物组成、化学成分和成因特征等方面进行对比分析。结果表明,以上三地糖白玉的主要矿物组成均为透闪石,次要矿物组成则各有不同。新疆、俄罗斯糖白玉以毛毡状变晶结构为主,青海糖白玉以纤维状变晶结构和纤维-隐晶质变晶结构为主;初步认定以上三地糖白玉的糖色为次生色,主要由褐铁矿导致。结合相关地质背景和风化作用特征,推测以上三地糖白玉不同的外观特征主要受玉体成矿后期和成矿期结束后周围环境变化的影响。

Comparative Analysis of Gemmological Characteristics of Brown-white Nephrites from Xinjiang,Qinghai and Russia

In order to identify the differences of structures,mineral components and genesis among the brown-white nephrites from Xinjiang,Qinghai in China and Russia,on the basis of appearance characteristics observation,this paper investigates the brown-white nephrite samples from Xinjiang,Qinghai in China and Russia by means of conventional gemmological methods,polarizing microscope,XRD and EPMA,and carries out a comparative analysis of structures,mineral components,chemical compositions and formation reasons.The results show that the main mineral component of the brown-white nephrite samples is tremolite while the secondary mineral component is different.The brown-white nephrite samples from Xinjiang in China and Russia have felt-like interweaving texture while the brown-white nephrite samples from Qinghai in China has fibrous blastic and fibrous cryptocrystalline texture.Brown is the secondary colour,which is caused by limonite.According to the related geological background and weathering features,it can be inferred that the different appearance characteristics of the brown-white nephrite from three localities are mainly influenced by the surrounding environment changes after the later stage and finishing stage of metallogenic period of nephrite.