黄色和红色石英质玉石的颜色成因研究

Coloration of yellow and red colored quartzite jade

石英质玉石是由隐晶质-微显晶质石英矿物集合体组成的一种玉石,黄色和红色是石英质玉石最主要的颜色种类,近年来在珠宝市场上备受关注。前人研究结果表明,黄色石英质玉石的致色矿物颗粒非常细小,赋存于石英颗粒之间,通过一般的测试方法很难准确鉴定其种属。本文对云南龙陵、安徽霍山、广西贺州3个产地的石英质玉石进行了显微镜观察、拉曼光谱和紫外可见光吸收光谱测试,通过紫外可见光吸收光谱的一阶导数图谱,对石英质玉石的黄色和红色部位进行了研究。结果表明,黄色石英质玉石紫外可见光吸收光谱一阶导数图谱的特征峰有545-535 nm和435 nm,主要由针铁矿致色;红色石英质玉石紫外可见光吸收光谱一阶导数图谱的特征峰介于555-595nm之间,主要由赤铁矿致色;黄色和红色之间的过渡色可同时出现595-555 nm、545-535 nm和435 nm特征峰,主要由针铁矿和赤铁矿共同致色。

Quartzite jade consists of tiny grained quartz crystallites, and the yellow color is the major color. However, due to lack of conclusive evidence and spectroscopic data, the coloration for the yellow color is unclear, although previous studies suggested that the yellow colored quartzite jade could be related to a very small quantity of nano-sized minerals. In this paper, yellow and red colored quartzite jades were collected from Longling of Yunnan Province, Huoshan of Anhui Province and Hezhou of Guangxi, and the coloration-related spectroscopic data were firstly obtained using the UV-Vis spectroscopic technique with first order derivative. It is found that the yellow colored quartzite jade is caused by goethite with characteristic absorption bands centered on 545-535, and 435 nm, and that the red colored quartzite jade is caused by hematite with absorption bands centered on 595-555 nm. For the mixed yellowish-red or reddish-yellow colouration, the first-order derivatives of the UV-Vis spectra show absorption bands centred on 595-555, 545-535, and 435 nm, indicating that the coloration results from a combination of hematite and goethite.