山西新发现大理岩玉的宝石矿物学特征

Gemmological and Mineralogical Characteristics of A New Kind of Marble Jade from Shanxi Province

山西北部六棱山地区新发现了一种玉石品种——大理岩玉,其主要有黄色和黄褐色两种颜色,结构较致密,透明度较好,是一种优质的饰面石材和玉雕原料。采用薄片观察、环境扫描电子显微镜、X射线粉末衍射、LA-ICP-MS和常规宝石学仪器等测试手段对该大理岩玉样品的宝石矿物学特征进行了测试与研究。结果显示,该大理岩玉为经变质作用形成的方解石大理岩,所含CaCO3的质量分数为96%～97%,推测Fe元素是该玉石的致色元素;微量的碳质和铁质粉末阻碍了柱状方解石的重结晶,形成条纹结构;方解石为不规则的多边形柱体,呈镶嵌的不规则他形变晶结构。通过分析大理岩玉的结构特征,认为平行于其层纹方向切磨,可使得其成品表面光洁度好,光泽强,不易破损。

A new kind of marble jade with mainly two colours,yellow and yellowish-brown,is found in Liuleng Mountain in the north of Shanxi Province.It is a kind of high-quality facing stone and jade carving material with compact structure and good transparency.The gemmological and mineralogical characteristics of the marble jade samples are studied by using the slice observation,environmental scanning electron microscopy,X-ray powder diffraction,LA-ICP-MS and conventional gemmological methods.The results show that the jade is a kind of marble transformed by metamorphism,in which the content of CaCO3 is between 96% and 97%.And probably,it is Fe that determines its colour.Furthermore,trace amounts of carbon and iron powders obstruct the recrystallization process of columnar calcite,resulting in the perthitic texture.And the calcite column,proved to be irregular xenoblastic texture,is irregular polygon cylinder.By analyzing the jade＇s structure features,this paper concludes that the marble jade product possesses the advantages of smooth surface,strong luster and being not easy to be broken when it is cut in parallel to the stripe direction.