Study on the Spectral Characteristics of Scapolite From Madagascar
DING Wei1, CHEN Quan-li1, 2*, AI Su-jie1, YIN Zuo-wei1
1. Gemmological Institute，China University of Geosciences（Wuhan），Wuhan 430074，China
2. Institute of Jewelry, West Yunnan University of Technology, Tengchong 679118, China
Abstract：The gemological and spectroscopic properties of the Madagascar scapolite is studied based on analyses of fifteen samples using EMPA, FTIR, Raman spectroscopy, UV-Vis Spectroscopy, fluorescence spectroscopy and some gemological instruments. The gemological characteristics of Madagascar scapolite are consistent with the theoretical values of scapolite; The samples are uniform in color and have a glassy luster. The raw stone crystal is relatively intact. Longitudinal stripes and maroon impurities are commonly seen on the surface of them. Iridescence can be seen on the surface of some samples, and a variety of inclusions can be seen inside the samples, such as biotite and colorless crystal inclusions. The infrared spectrum analysis shows that absorption peaks of 1 039, 1 105, 1 196 cm-1 in the fingerprint area are attributed to the Si(Al)—O group. 752 cm-1 peak is due to Si—Si(Al) stretching, 551, 687, 624 cm-1 peaks are due to O—Si (Al)—O bending vibration. Bending vibration of Si—O—Si associated with Na(Ca) —O stretching jointly results in a 459 cm-1 peak. 416 cm-1 is due to the bending vibration of Si—O—Si. Absorption peaks related to functional group area are mainly due to different vibrational modes and frequencies of CO2-3 (2 499, 2 629, 2 964 cm-1) and O—H(3 530 and 3 592 cm-1), which are diagnostic for the identification of scapolite. The Raman Spectroscopic analysis indicates that the bending vibration of bridge oxygen produces 459 and 538 cm-1 peaks; Al—O vibration leads to a 775 cm-1 peak. The vibration of SiO4 tetrahedron unit generates 1 114 cm-1. UV-Vis spectrum shows 379 and 420 nm, which are caused by electron transfer between Fe2+ and Fe3+ in tetrahedron position. The yellow color of Madagascar scapolite is due to transition metal elements. The intensity of the 420 nm peak directly affects the color depth of scapolite. Analysis of 3D luminescence shows a relatively uniform luminescence phenomenon, which shows two fluorescence peaks, one strong and one weak, mostly centered at 302 nm(λex)/343 nm(λem). The EMPA analysis result indicates that the sample belongs to Dipyre in the scapolite series. The Ma value is around 66%~69%, and the average value is 68.1%, and with the increase of the Ma value, the refractive index decreases. As a nondestructive testing technique, spectrum testing is suitable for identifying gem varieties. It is of great significance for the identification of Madagascar scapolite. It provides data support for the traceability of origin and the differentiation of scapolite varieties.
丁 薇，陈全莉，艾苏洁，尹作为. 马达加斯加黄色方柱石的谱学特征研究[J]. 光谱学与光谱分析, 2022, 42(07): 2194-2199.
DING Wei, CHEN Quan-li, AI Su-jie, YIN Zuo-wei. Study on the Spectral Characteristics of Scapolite From Madagascar. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2022, 42(07): 2194-2199.
