Li Niu, Guo Qingfeng, Wang Qianqian, Liao Libing
School of Gemmology, China University of Geosciences Beijing 100083 China
Jewelry and Mineral Materials Laboratory of Experimental Teaching Demonstration Center Beijing China.
RSC Adv. 2022 Oct 25;12(47):30416-30425. doi: 10.1039/d2ra04197a. eCollection 2022 Oct 24.
The structure type and water content of opal will affect its stability and value. When the structure is Opal-A type, its value is higher. When the water content is high, its stability will decrease. The structural attribution and water distribution of pink, yellow, green, blue and purple opal have been investigated by several methodologies like powder X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Fourier transform near infrared spectroscopy (FT-NIR). The results show that all the opal samples are CT type, among which the green sample has the highest crystallinity. The water contents of the opals range from 3.06 to 8.78%. The distribution and quantity of molecular water (HO) and silanols (HO) are calculated semi-quantitatively according to intensity of 4500 cm and 5200 cm peaks in the near infrared region, and it is found that the water in all the samples is basically composed of molecular water. The precipitation mechanism for opal formation results in different structural types, and the difference in structural composition leads to different water contents. This work provides a theoretical basis for the future study of the opal metallogenic environment.
蛋白石的结构类型和含水量会影响其稳定性和价值。当结构为蛋白石-A型时，其价值较高。当含水量较高时，其稳定性会降低。通过粉末X射线衍射（XRD）、扫描电子显微镜（SEM）、热重分析（TGA）和傅里叶变换近红外光谱（FT-NIR）等多种方法研究了粉色、黄色、绿色、蓝色和紫色蛋白石的结构归属和水分布。结果表明，所有蛋白石样品均为CT型，其中绿色样品的结晶度最高。蛋白石的含水量在3.06%至8.78%之间。根据近红外区域4500 cm和5200 cm峰的强度半定量计算分子水（HO）和硅醇（HO）的分布和数量，发现所有样品中的水基本由分子水组成。蛋白石形成的沉淀机制导致不同的结构类型，结构组成的差异导致不同的含水量。这项工作为未来蛋白石成矿环境的研究提供了理论依据。
