Introduction
Guangyuanite, ideally Pb3Cl3(Se4+O3)(OH), is a new mineral species discovered from the El Dragón mine, Antonio Quijarro Province, Potosí Department, Bolivia. It is named in honour of the late Chinese mineralogist, Prof. Chen Guangyuan (1920–1999). Prof. Chen obtained his Degree of Licentiate from the Uppsala University of Sweden in 1951 and became a teacher and researcher at Peking University between 1951 and 1952 and later at the China University of Geosciences in Beijing from 1952 to 1999. Prof. Chen is regarded as the pioneer and leader for both teaching and research in genetic and exploration mineralogy in China from the 1950's to 1980's. He made significant contributions to the systematic studies of the genesis of minerals, especially on genetic classification of mineral groups, typomorphic mineralogy, and mineralogical mapping for exploration, with over 100 publications and 9 books, including the well-recognised “Genetic Mineralogy and Prospecting Mineralogy”, which has been adopted by many universities in China. The new mineral and its name (symbol Gyn) have been approved by the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA 2022-124, Yang et al., Reference Yang, Gu, McGlasson and Gibbs2023d). The co-type samples have been deposited at the University of Arizona Alfie Norville Gem and Mineral Museum (Catalogue # 22714) and the RRUFF Project (deposition # R210013) (http://rruff.info) (Lafuente et al., Reference Lafuente, Downs, Yang, Stone, Armbruster and Danisi2015).
Lead chloride selenite minerals are rather rare in Nature and only six minerals contain Pb–Cl–(Se4+O3)2– in the current IMA-approved mineral list (Table 1). Interestingly, all of these minerals have only been described in the past 25 years. Nevertheless, synthetic lead chloride selenite materials have been an attractive subject in numerous investigations. On the one hand, selenite materials can form a diversity of unusual structures due to the presence of the stereochemically active lone-pair electrons in Se4+, which can serve as structure-directing agents (Berdonosov et al., Reference Berdonosov, Stefanovitch and Dolgikh2000, Reference Berdonosov, Olenev and Dolgikh2012; Wickleder, Reference Wickleder2002 and references therein). The lone-pair electrons in Se4+ are not involved in the formation of chemical bonds, thus acting like terminal ligands and resulting in various voids in the structure. Furthermore, the asymmetric coordination of (Se4+O3)2– (trigonal pyramid) may also give rise to noncentrosymmetric structures with interesting physical properties, such as nonlinear optical second-harmonic generation, piezoelectric, ferroelectric and pyroelectric properties (Porter et al., Reference Porter, Ok, Bhuvanesh and Halasyamani2001; Ok et al., Reference Ok, Bhuvanesh and Halasyamani2001; Ok and Halasyamani, Reference Ok and Halasyamani2002; Kong et al., Reference Kong, Huang, Sun, Mao and Cheng2006; Kim et al., Reference Kim, Yeon and Halasyamani2009, Reference Kim, Kim, Chang, Halasyamani and Ok2010). Conceivably, introduction of other cations with lone-pair electrons into selenite materials (such as Tl+, Sn2+, Pb2+, Sb3+ and Bi3+) will offer more new phases from which additional functionalities may arise (Ok et al., Reference Ok, Bhuvanesh and Halasyamani2001; Porter et al., Reference Porter, Ok, Bhuvanesh and Halasyamani2001; Dityatyev et al. Reference Dityatyev, Smidt, Stefanovich, Lightfoot, Dolgikh and Opperman2004; Krivovichev et al., Reference Krivovichev, Avdontseva and Burns2004; Kim et al. Reference Kim, Yeon and Halasyamani2009; Zhang et al., Reference Zhang, Hu, Li, Jiang and Jiang-Gao Mao2012). On the other hand, because both Se4+ and X - (X = Cl, Br and I) can act as ‘chemical scissors’ (Johnsson et al., Reference Johnsson, Törnroos, Mila and Millet2000, Reference Johnsson, Törnroos, Lemmens and Millet2003; Millet et al., Reference Millet, Johnsson, Pashchenko, Ksari, Stepanov and Mila2001), considerable effort has also been made to incorporate X – anions into selenite materials to obtain low dimensional structures, which has resulted in a number of compounds with fascinating magnetic properties (e.g. Becker et al., Reference Becker, Johnsson, Kremer, Klauss and Lemmens2006, Reference Becker, Prester, Berger, Lin, Johnsson, Drobac and Zivkovic2007; Jiang and Mao, Reference Jiang and Mao2006; Zhang et al., Reference Zhang, Johnsson, Berger, Kremer, Wulferding and Lemmens2009, Reference Zhang, Berger, Kremer, Wulferding, Lemmens and Johnsson2010, Reference Zhang, Hu, Li, Jiang and Jiang-Gao Mao2012). Thus far, at least 10 different lead halide selenite phases have been synthesised and structurally characterised, including Pb3(SeO3)(SeO2OH)Cl3 (Porter et al., Reference Porter, Ok, Bhuvanesh and Halasyamani2001), Pb3(SeO3)2Cl2, Pb3(SeO3)2Br2, Pb3(SeO3)2I2, Pb2Cd3(SeO3)4I2(H2O) (Porter and Halasyamani, Reference Porter and Halasyamani2001; Berdonosov et al. Reference Berdonosov, Olenev and Dolgikh2012; Zhang et al., Reference Zhang, Hu, Li, Jiang and Jiang-Gao Mao2012), (Pb2Cu2+9O4)(SeO3)4(Cu+Cl2)Cl5, (PbCu2+5O2)(SeO3)2(Cu+Cl2)Cl3, and (PbxCu2+(6−x)O2)(SeO3)2(Cu+Cl2)K(1−x)Cl(4−x) (x = 0.20) (Kovrugin et al., Reference Kovrugin, Colmont, Siidra, Mentré, Al-Shuray, Gurzhiy and Krivovichev2015), (Cu2+Pb6(SeO3)4Br6, Cu2+Pb2(SeO3)2Br2, Cu2+3Pb2.4(SeO3)5Br0.8, Cu2+2Pb(SeO3)2Br2, Cu2+4Pb(SeO3)4Br2, [Cu2+9Pb2O4](Cu+Br2)(SeO3)4Br5, [Cu2+7PbO3](Cu+Br)0.35(SeO3)3Br4, [Cu2+8Pb2O4](Cu+Br)1.5(SeO3)4Br4, [Cu2+6Pb3O4](Cu+Pb1.27Br3.54)(SeO3)4Br2) (Siidra et al., Reference Siidra, Kozin, Depmeier, Kayukov and Kovrugin2018), Pb2Cd(SeO3)2X 2 (Gong et al. Reference Gong, Hu, Ma, Mao and Kong2019), Pb3(SeO3)(HSeO3)Br3, Pb3(SeO3)(OH)Br3 and CdPb8(SeO3)4Cl4Br6 (Shang and Halasyamani, Reference Shang and Halasyamani2020). In all these compounds, Se4+ only forms bonds with O atoms, whereas Pb2+ can form bonds with both X and O atoms. This paper describes the physical and chemical properties of guangyuanite, and its crystal structure determined from single-crystal X-ray diffraction data.
References: (1) Vergasova et al. (Reference Vergasova, Krivovichev, Britvin, Fitatov, Berns and Ananyev2005); (2) This study; (3) Demartin et al. (Reference Demartin, Gramaccioli and Pilati2003); (4) Shuvalov et al. (Reference Shuvalov, Vergasova, Semenova, Filatov, Krivovichev, Siidra and Rudashevsky2013); (5) Gemmi et al. (Reference Gemmi, Campostrini, Demartin, Gorelik and Gramaccioli2012); (6) Porter et al. (Reference Porter, Ok, Bhuvanesh and Halasyamani2001); (7) Yang et al. (Reference Yang, Gu, Gibbs and Downs2023a).
Sample description and experimental methods
Occurrence, physical and chemical properties, and Raman spectra
Guangyuanite was found on a specimen (Fig. 1) collected from the El Dragón mine (19°49’15’’S, 65°55’0’’W), Antonio Quijarro Province, Potosí Department, Bolivia. Associated minerals are Co-bearing krut'aite–penroseite, chalcomenite, schmiederite, olsacherite, phosgenite, anglesite, cerussite and franksousaite. Detailed descriptions on the geology and mineralogy of the El Dragón mine were given by Grundmann et al. (Reference Grundmann, Lehrberger and Schnorrer-Köhler1990, Reference Grundmann, Lehrberger and Schnorrer-Köhler2007) and Grundmann and Förster (Reference Grundmann and Förster2017). This is an epithermal deposit consisting of a single selenide vein hosted by sandstones and shales. The major ore mineral is krut'aite, CuSe2, varying in composition to penroseite, NiSe2. Later solutions rich in Bi, Pb and Hg resulted in the crystallisation of minerals such as clausthalite, petrovicite, watkinsonite and the recently described minerals eldragónite, Cu6BiSe4(Se2) (Paar et al., Reference Paar, Cooper, Moëlo, Stanley, Putz, Topa, Roberts, Stirling, Raith and Rowe2012), grundmannite, CuBiSe2 (Förster et al., Reference Förster, Bindi and Stanley2016), hansblockite, (Cu,Hg)(Bi,Pb)Se2 (Förster et al., Reference Förster, Bindi, Stanley and Grundmann2017), cerromojonite, CuPbBiSe3 (Förster et al., Reference Förster, Bindi, Grundmann and Stanley2018) and nickeltyrrellite, CuNi2Se4 (Förster et al., Reference Förster, Ma, Grundmann, Bindi and Stanley2019). Oxidation produced a wide range of secondary Se-bearing minerals, such as favreauite, PbBiCu6O4(SeO3)4(OH)⋅H2O (Mills et al., Reference Mills, Kampf, Housley, Christy, Thorne, Chen and Steele2014), alfredopetrovite, Al2(Se4+O3)3⋅6H2O (Kampf et al., Reference Kampf, Mills, Nash, Thorne and Favreau2016b), franksousaite, PbCu(Se6+O4)(OH)2 (Yang et al., Reference Yang and McGlasson2022), bernardevansite, Al2(Se4+O3)3⋅6H2O (Yang et al., Reference Yang, Gu, Jenkins, Gibbs and Downs2023b), petermegawite, Al6(Se4+O3)3[SiO3(OH)](OH)9⋅10H2O (Yang et al., Reference Yang, Gu, Jenkins, Gibbs, McGlasson and Scott2023c) and the new mineral guangyuanite, described herein.
Guangyuanite occurs as equant brown-yellowish crystals (Fig. 2) in a vug, where only two crystals were found. The matrix consists of Co-bearing krut'aite–penroseite. Individual crystals of guangyuanite are up to 0.40 × 0.30 × 0.30 mm. Guangyuanite is pale yellow–brown in transmitted light, transparent with white streak and vitreous lustre. It is brittle and has a Mohs hardness of ~3. No cleavage was observed. The density could not be measured because it is greater than available high-density liquids and there is insufficient material for the direct measurement. The calculated density is 6.73 g/cm3 on the basis of the empirical chemical formula and unit cell volume from single-crystal X-ray diffraction data. No optical data were measured because the indices of refraction are too high for measurement with available index liquids. The calculated average index of refraction is 2.04 for the empirical formula based on the Gladstone-Dale relationship (Mandarino, Reference Mandarino1981). Guangyuanite is insoluble in water and hydrochloric acid.
The chemical composition was determined using a Shimadzu-1720 electron microprobe (WDS mode, 15 kV, 10 nA, and a beam diameter of 2 μm). The standards used for the probe analysis are given in Table 2, along with the determined compositions (6 analysis points). The resultant chemical formula, calculated on the basis of 7 (O,Cl) atoms per formula unit (from the structure determination), is Pb3.02Cl3(Se4+0.99O3)(OH), which can be simplified to Pb3Cl3(Se4+O3)(OH). The ideal formula requires (wt.%) PbO 76.80, SeO2 12.73, H2O 1.03, Cl 12.20, O ≡ Cl –2.76, total 100 wt.%.
The Raman spectrum of guangyuanite (Fig. 3) was collected on a randomly oriented crystal with a Thermo Almega microRaman system, using a solid-state laser with a wavelength of 532 nm at 50% of 150 mW power and a thermoelectric cooled CCD detector. The laser is partially polarised with 4 cm–1 resolution and a spot size of 1 μm.
X-ray crystallography
Both the powder and single-crystal X-ray diffraction data for guangyuanite were collected on a Rigaku Xtalab Synergy D/S 4-circle diffractometer. Powder X-ray diffraction data were collected with CuKα radiation in the Gandolfi powder mode at 50 kV and 1 mA (Table 3) and the unit-cell parameters were refined using the program by Holland and Redfern (Reference Holland and Redfern1997): a = 10.9920(6), b = 10.6387(7), c = 7.7863(5) Å, and V = 910.55(6) Å3.
Note: The strongest lines are given in bold.
Single-crystal X-ray diffraction data of guangyuanite were collected with MoKα radiation from a 0.05 × 0.05 × 0.04 mm fragment. The systematic absences of reflections suggest possible space group Pn21a or Pnma. The structure was solved and refined using SHELX2019 (Sheldrick, Reference Sheldrick2015a, Reference Sheldrick2015b) based on space group Pnma, because it produced better refinement statistics in terms of bond lengths and angles, atomic displacement parameters, and R factors. The H atom was located through difference-Fourier syntheses. The positions of all atoms were refined with anisotropic displacement parameters, except for the H atom, which was refined with the U iso set to 1.5 times that of O3 on which it rides. The refinement statistics are given in Table 4. Final atomic coordinates and displacement parameters are given in Tables 5 and 6, respectively. Selected bond lengths are presented in Table 7. The bond valences were calculated using the parameters given by Brown (Reference Brown2009) (Table 8). The crystallographic information file has been deposited with the Principal Editor of Mineralogical Magazine and is available as Supplementary material (see below).
Note: X = Cl and Br for guangyuanite and the Br-analogue, respectively. Data for the Br-analogue were taken from Shang and Halasyamani (Reference Shang and Halasyamani2020)
Note: superscripts indicate the number of equivalent bonds for the respective sum arrowed.
Crystal structure description and discussion
Guangyuanite is isotypic with synthetic Pb3Br3(Se4+O3)(OH) (Shang and Halasyamani, Reference Shang and Halasyamani2020). Its structure contains two symmetrically distinct Pb (Pb1 and Pb2), two Cl (Cl1 an Cl2), one Se, one H and three O (O1, O2 and O3) atoms, among which O3 is hydroxyl (OH) (Table 8) and forms the hydrogen bond with O2 (Table 7). The Pb1 cation is in a polyhedron coordinated by 4O and 4Cl atoms (Fig. 4a), whereas the Pb2 cation is only bonded by six anions (3O + 3Cl) (Fig. 4b), forming a marked one-sided coordination typical of Pb2+ with a stereochemically-active 6s2 lone-electron pair. The Se4+ cation is bonded to three O atoms, giving rise to the typical [Se4+O3] trigonal pyramid.
The crystal structure of guangyuanite can be described as consisting of layers of edge-sharing [Pb1O4Cl4] polyhedra parallel to (100) (Fig. 5). These layers are linked together by sharing polyhedral corners (Cl atoms), as well as [Pb2O3Cl3] and [Se4+O3] groups (Fig. 6). The [PbO4Cl4] polyhedra are apparently a basic structural unit in many lead oxychlorides, as observed in nadorite, PbSbO2Cl (Giuseppetti and Tadini, Reference Giuseppetti and Tadini1973), perite, PbBiO2Cl (Gillberg, Reference Gillberg1960), diaboleite, CuPb2Cl2(OH)4 (Cooper and Hawthorne, Reference Cooper and Hawthorne1995), hematophanite Pb4Fe3+3O8(Cl,OH), (Rouse, Reference Rouse1973) and chloroxiphite Pb3CuO2Cl2(OH)2 (Finney et al., Reference Finney, Graeber, Rosenzweig and Hamilton1977; Siidra et al., Reference Siidra, Krivovichev, Turner and Rumsey2008).
According to Raman or IR spectroscopic studies on hydrous materials containing (SeO3)2– (e.g. Wickleder et al., Reference Wickleder, Buchner, Wickleder, Sheik, Brunklaus and Eckert2004; Frost et al., Reference Frost, Weier, Reddy and Cejka2006; Frost and Keeffe, Reference Frost and Keeffe2008; Djemel et al., Reference Djemel, Abdelhedi, Ktari and Dammak2013; Kasatkin et al., Reference Kasatkin, Plášil, Marty, Agakhanov, Belakovskiy and Lykova2014; Mills et al., Reference Mills, Kampf, Housley, Christy, Thorne, Chen and Steele2014; Kampf et al., Reference Kampf, Mills and Nash2016a; Shang and Halasyamani, Reference Shang and Halasyamani2020), we made the following tentative assignments of major Raman bands for guangyuanite. The broad weak bands between 2850 and 3300 cm–1 (centred at 3130 cm–1) are due to the O–H stretching modes in OH groups. The bands between 665 and 1000 cm–1 are ascribable to the Se4+–O stretching vibrations within the Se4+O3 groups, whereas those from 320 to 570 cm–1 originate from the O–Se4+–O bending modes. The bands below 320 cm–1 are associated mainly with the rotational and translational modes of Se4+O3 groups, as well as the Pb–O and Pb–Cl interactions and lattice vibrational modes.
The calculated bond-valence sums for guangyuanite (Table 8) indicate that O3 is the OH group, which forms a hydrogen bond with O2, with the O3···O2 distance of 2.707 Å (Table 7). According to the correlation between νO–H and O—H···O distances for minerals (Libowitzky, Reference Libowitzky1999), the Raman band centred at 3130 cm–1 corresponds well with the O···O distances between 2.70 and 2.80 Å. In comparison, the O–H stretching band is centred at 3201 cm–1 for isostructural Pb3Br3(Se4+O3)(OH) (Shang and Halasyamani, Reference Shang and Halasyamani2020), which has an O—H⋅⋅⋅O distance of 2.842 Å (Table 7). Because of similarities in both chemistry and structure between guangyuanite and orlandiite, Pb3Cl4(Se4+O3)⋅H2O (Table 4), the Raman spectrum of orlandiite from the RRUFF Project (http://rruff.info/R100122) is also plotted in Fig. 3 for comparison. Evidently, the spectra of two minerals are very alike below 1000 cm–1.
Guangyuanite is one of six lead selenite chloride minerals documented thus far (Table 1), after allochalcoselite Cu1+Cu2+5PbO2(SeO3)2Cl5, orlandiite Pb3Cl4(Se4+O3)⋅H2O, prewittite KPb1.5ZnCu6O2(SeO3)2Cl10, sarrabusite Pb5CuCl4(SeO3)4 and wangkuirenite Pb3Cl2(Se4+O3)2. Chemically, guangyuanite is very similar to orlandiite, the only hydrated mineral in this group. Interestingly, Porter et al. (Reference Porter, Ok, Bhuvanesh and Halasyamani2001) synthesised two lead selenite chlorides: Pb3Cl3(SeO3)(SeO2OH) and Pb3Cl2(SeO3)2, both of which are pseudo-layered, consisting of sheets of lead oxychloride polyhedra linked to (Se4+O3)2–. The latter has been discovered recently in Nature as wangkuirenite (Yang et al., Reference Yang, Gu, Gibbs and Downs2023a), whereas the former has a chemical formula similar to that of guangyuanite. In fact, guangyuanite may be obtained from this compound by removing the Se4+O2 molecule. As both Pb3Cl3(SeO3)(SeO2OH) and Pb3Cl2(SeO3)2 (wangkuirenite) can be readily synthesised using a low-temperature (160°C) aqueous method (Porter et al., Reference Porter, Ok, Bhuvanesh and Halasyamani2001), the former compound may be found in Nature as well someday.
Acknowledgements
We are grateful for the constructive comments by Dr. Luca Bindi, Dr. Peter Leverett, and an anonymous reviewer. This study was funded by the Feinglos family and Mr. Michael M. Scott.
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1180/mgm.2023.93.
Competing interests
The authors declare none.