西藏东部钙铬榴石的矿物学特征及呈色机理

钙铬榴石是石榴石族中的稀有品种,文中对近年新发现的西藏东部钙铬榴石样品进行了矿物学特征分析和呈色机理探讨。采用扫描电镜观察钙铬榴石样品的显微结构并进行能谱分析,结果表明其内部含有颗粒很小的铬铁矿和石英包裹体,以及裂隙中充填的方解石和与钙铬榴石为类质同象连续关系的钙铝榴石,从而为该钙铬榴石的夕卡岩成因和产状提供了佐证。采用紫外-可见光分光光度计对样品进行吸收光谱测试,对其颜色指数进行了定量分析,所得样品颜色的主波长为530～540nm,饱和度为80%左右,进而分析了钙铬榴石的颜色主要由Cr3+引起,其呈色机理归因于Cr3+的d轨道电子跃迁。

Mineralogical characteristics and the coloring mechanism of uvarovite from eastern Tibet, China

Uvarovite is a rare species of the garnet group.The mineralogical characteristics and coloring mechanism of uvarovite from eastern Tibet were systematically investigated and results are reported in this article.The microstructure of an uvarovite sample was analyzed using SEM methods.Tiny quartz and chromite inclusions,calcite filling in microfractures and grossularite that forms a solid solution with uvarovite were discovered in the sample.This demonstrates that the uvarovite of eastern Tibet is of skarn origin.The spectral characteristics of the uvarovite were investigated using UV-VIS absorption spectrometry.This showed that the main peak position of the transmission light is between 530-540 nm,and the color saturation is about 80%.The dense green color of the uvarovite sample is caused by its higher color saturation.The theoretical analysis of the mechanism of the green coloring of uvarovite indicates that the transition of 3d-orbital electron in the Cr3+ is responsible for the green color.