1. Gemmological Institute of China University of Geosciences (Wuhan), Wuhan 430074, China
2. Hubei Gems and Jewelry Engineering Technology Research Center, Wuhan 430074, China
3. School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275, China
Abstract：Rhodonite is a characteristic pink single-chain silicate mineral. As the gem-quality transparent rhodonite is rare, rhodonite is often produced as dense massive aggregate, which is usually classified as common jade in the gem trade. Monocrystal rhodonite is represented by the Broken Hill mining area in Australia and the Minas Gerais mining area in Brazil. In this paper, 10 samples of monocrystal rhodonite from Brazil are used for the LA-ICP-MS test, Raman spectroscopy test, infrared absorption spectroscopy test and UV-Vis absorption spectroscopy test, aiming to explore the chemical composition and spectroscopic characterization of rhodonite and provide basic data for the identification, optimization and origin identification of rhodonite. According to the results of LA-ICP-MS, the average crystal structure chemical formula of the samples is (Mn0.763Ca0.106Fe0.070 Mg0.061)1.00SiO3. The main elements are rich Mn and Ca-Fe-Mg, similar to the monocrystal rhodonite composition produced in Minas Gerais, Brazil. The Raman shift of the sample is mainly composed of 666 cm-1 strongest peak, 972, 997 cm-1 double-peak, and several weak peaks. Which are related to the stretching and bending vibration of [SiO4] tetrahedral groups and the stretching vibration of octahedral coordination cations. Infrared test results show that the absorption peak of rhodonite in the fingerprint region is mainly due to the stretching and bending vibration of Si—O. The structure of rhodonite determines that there are five absorption peaks in the band of 750～550 cm-1, which distinguishespyroxenes and pyroxenoids minerals. There is an obvious absorption peak at 3 631 cm-1 in the near-infrared region, which is a typical OH stretching vibration band indicating that the sample contains a small amount of structural water. UV-Vis absorption spectra show that rhodonite is a typical self-colored mineral, mainly attributed to the d—d electronic transition of octahedral coordination Mn2+. The absorption peak is located at the purple and yellow-green regions, which is the main reason for the orange-pink color of the samples.
Key words：Monocrystal rhodonite from Brazil; LA-ICP-MS; Infrared spectrum; Mn2+ coloration
[1] ZHANG Bei-li(张蓓莉). Systematic Gemology(系统宝石学). Beijing: Geology Press(北京: 地质出版社), 2006: 428.
[2] Millsteed P W, Mernagh T P, Otieno-Alego V, et al. Gems & Gemology, 2005, 41(3): 246.
[3] Quinn E P. Gems & Gemology, 2004, 40(3): 260.
[4] Leverett P, Williams P A. The Mineralogical Record, 2008, 39(2): 125.
[5] Cooper A. Gems & Gemology, 2021, 57(2): 154.
[6] ZHU Hong-wei, LI Ting, YAN Fei(朱红伟，李 婷，燕 菲). Journal of Gems & Gemmology(宝石与宝石学杂志), 2017, 19(S1): 35.
[7] Nelson W R, Griffen D T. American Mineralogist, 2005, 90: 969.
[8] DENG Ming-guo, XU Rong, WANG Peng, et al(邓明国，徐 荣，王 朋，等). Acta Petrologica Sinica(岩石学报), 2016, 32(8): 2248.
[9] Diella V, Adamo I, Bocchio R. Periodico di Mineralogia, 2014, 83(2): 207.
[10] Caucia F, Marinoni L, Riccardi M P, et al. Gems & Gemology, 2020, 56(1): 110.
[11] Mills S J, Frost R L, Kloprogge J T, et al. Spectrochimica Acta, 2005, 62(1-3): 171.
[12] Buzatu A, Buzgar N. Analele Stiintifice de Universitatii AI Cuza din Iasi, 2010, 56(1): 121.
[13] Jovanovski G, Makreski P, Kaitner B, et al. Crotica Chemica Acta, 2009, 82(2): 375.
[14] Skogby H, Bell D R, Rossman G R. American Mineralogist, 1990, 75(7-8): 764.
[15] YUAN Wen, HOU Guang-shun, ZHANG Yan-lin, et al(袁 稳，侯广顺，张艳林，等). Acta Mineralogica Sinica(矿物学报), 2022, 42(1): 29.
[16] Manning P G. The Canadian Mineralogist, 1968, 9(3): 348.
