“米黄玉”的宝石矿物学特征

湖北省郧县产有一种矿石,因其色如黄米而俗称为＂米黄玉＂,其质细腻柔润、色泽纯净剔透。本研究选取6件＂米黄玉＂样品,采用常规宝石学方法、薄片观察、红外光谱、X射线粉末衍射、LA-ICP-MS等测试手段,对其矿物学、宝石学和谱学特征进行了研究,并对其品质评价进行了探讨。结果显示,＂米黄玉＂样品的组分纯净,结构呈短柱状晶体镶嵌排列,单个晶体的颗粒大小在长0.240~0.880 mm、宽0.064~0.160 mm范围内波动,并呈定向排列;其主要化学成分为CaCO3,含少量的MgCO3,成分纯净,杂质元素较少。依照GB/T 16552—2003《珠宝玉石名称》,对宝石级＂米黄玉＂应直接采用＂大理石＂的名称,可在备注中注明：俗称＂米黄玉＂。

Gemmological and Mineralogical Characteristics of ＂Beige Jade＂

A kind of mineral occurs in Yunxian,Hubei province,naming ＂Beige jade＂ by its colour appearance.It is known as its delicate quality and pure colour.The mineralogical,gemmological and spectral characteristics of six ＂Beige jade＂ samples are studied by means of the conventional gemmological methods,the slice observation,infrared spectrometer,XRD and LA-ICP-MS.The results indicate that the structure of ＂Beige jade＂ samples is in mosaic arrangement of short prismatic crystals with its size in the range of 0.240—0.880 mm in length and 0.064—0.160 mm in width,showing the orientate arrangement.The main chemical compositions of the samples are CaCO3,containing a small number of MgCO3 and less impurity.According to GB/T 16552—2003 GemsNomenclature,the gem-quality ＂Beige jade＂ should be directly named as ＂marble＂ and explained as ＂popular name：＇Beige jade＇＂ in the notes.