新疆黑青色蛇纹石玉的宝石学特征及颜色成因

Gemological Characteristics and Color Origin of Black Cyan Serpentine from Xinjiang Region

新疆黑青色蛇纹石玉是近期市场上新出现一种玉石品种,相对于其他颜色的蛇纹石玉,人们对它的认识较为薄弱。以新疆黑青色蛇纹石玉为研究对象,在对其常规宝石学特征以及偏光显微镜下研究的基础上,利用X射线粉晶衍射技术、电子探针分析以及红外光谱、拉曼光谱、紫外可见光谱等分析测试手段,对其矿物组成、化学成分、结构构造及谱学特征进行了系统研究,分析了其黑青色的致色原因。研究结果表明,黑青色蛇纹石玉的主要组成矿物为蛇纹石族矿物叶蛇纹石,少量为利蛇纹石、方解石和磁铁矿;蛇纹石具有富铁、贫镁的特点;结构为纤维状变晶结构,局部鳞片状变晶结构;其红外光谱和拉曼光谱特征与叶蛇纹石的谱学特征一致,黑青色主要与蛇纹石中Fe的含量有关。Fe^(3+) d-d电子跃迁以及Fe^(2+)→Fe^(3+)之间的电荷转移是蛇纹石玉呈黑青色的原因。

Xinjiang black cyan serpentine is a new jade variety that has recently appeared on the market,and people′s awareness of it is relatively weak compared to other colors of serpentine.In this paper,Xinjiang black cyan serpentine is taken as the research object.On the basis of its conventional gemmological characteristics and studies under polarized light microscope,its mineral composition,chemical composition,structures,textures and spectroscopic characteristics are systematically studied by using X-ray powder crystal diffraction technology,EPMA,and infrared spectroscopy,raman spectroscopy,UV-visible spectroscopy as analytical tests.At the same time,the cause of its black cyan coloration is also analyzed.The results show that the main constituent minerals of black cyan serpentine are the serpentine group minerals antigorite,with a small amount of lizardite,calcite and magnetite.Serpentine is rich in iron and poor in magnesium.Black cyan serpentine is mainly of fibrous metamorphic structure,locally with scale-like metamorphic structure.Its infrared and raman spectral characteristics are consistent with those of antigorite,and the black cyan color is mainly related to the content of Fe in serpentine.The black cyan color of serpentine is due to Fe 3+d-d electron transition and charge transfer between Fe 2+→Fe 3+.