Author Accepted Manuscript DOI: 10.1177/0003702820984254

Systematic Raman Spectroscopic Study of the Isomorphy Between the Arsenate Roselite, Wendwilsonite, Zincroselite, Brandtite, and Rruffite.

Journal: Applied Spectroscopy

Manuscript ID ASP-20-0302.R1

ManuscriptPeer Type: Submitted Review Manuscript Version

Date Submitted by the 25-Nov-2020 Author:

Complete List of Authors: Kloprogge, J.; University of the Philippines Visayas, Chemistry; The University of Queensland - Saint Lucia Campus, School of Earth and Environmental Sciences

arsenate, roselite group, roselite, zincroselite, brandtite, wendwilsonite, Manuscript Keywords: rruffite, Raman spectroscopy

In nature a wide variety of minerals are known with the general formula X2M(TO4)2·2(H2O) and an important group is formed by minerals with T = As. Most of these occur as minor or trace minerals in environments such as hydrothermal alterations of primary sulfides and arsenides. X- ray Photoelectron Spectroscopy (XPS) and Raman microspectroscopy have been utilized to study the chemistry and of the roselite subgroup minerals, Ca2M(AsO4)2·2H2O (with M = Co, Mg, Mn, Zn, and Cu). The arsenate AsO4 stretching region exhibited minor differences between the roselite subgroup minerals, which can be explained by the ionic radius of the cation substituting on the M position in the structure. Multiple AsO4 antisymmetric stretching vibrations were found, pointing to a tetrahedral symmetry reduction. Similar observations were made for the corresponding bending modes. Bands around 450 cm-1 were attributed to ν4 bending modes. Several bands in Abstract: the 300–350cm-1 region attributed to ν2 bending modes also provide evidence of symmetry reduction of the AsO4 anion. Two broad bands for roselite were found around 3330 and 3120 cm-1 and were attributed to the OH stretching bands of crystal water. These bands are accompanied by two bands around 1700 and 1610 cm-1 attributed to the corresponding OH-bending modes. In conclusion, both XPS and Raman spectroscopy have been shown here to be valuable non-destructive analytical tools to characterize these secondary arsenate minerals. X-ray Photoelectron Spectroscopy and Raman microspectroscopy allow the chemistry and molecular structure of the roselite subgroup minerals to be studied in a non-destructive way. The minerals in the roselite subgroup are easily distinguished based on their chemical composition as determined by XPS. As expected for minerals with the same crystal structure, similarities exist in the Raman spectra, sufficient differences exist to be able to identify these minerals.

Applied Spectroscopy Page 1 of 36 Author Accepted Manuscript 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Peer Review Version 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Applied Spectroscopy Author Accepted Manuscript Page 2 of 36 1 2 3 4 Systematic Raman Spectroscopic Study of the Isomorphy Between the 5 6 Arsenate Minerals Roselite, Wendwilsonite, Zincroselite, Brandtite, and 7 8 Rruffite. 9 10 11 J. Theo Kloprogge1,2* 12 13 1 Department of Chemistry, College of Arts and Sciences, University of the Philippines Visayas, 14 15 Miag-ao, Iloilo 5023, Philippines 16 2 School of Earth and Environmental Sciences, The University of Queensland, Brisbane, Qld 17 Peer Review Version 18 4072, Australia 19 20 21 *Corresponding author email: 22 23 Email: [email protected] 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 1 59 60 Applied Spectroscopy Page 3 of 36 Author Accepted Manuscript 1 2 3 ABSTRACT 4 5 In nature numerous minerals are known with the general formula X2M(TO4)2·2(H2O) and an 6 7 important group is formed by minerals with T = As. Most of these occur as minor or trace 8 minerals in environments such as hydrothermal alterations of primary sulfides and arsenides. X- 9 10 ray photoelectron spectroscopy and Raman spectroscopy have been utilized to study the 11 12 chemistry and crystal structure of the roselite subgroup minerals, Ca2M(AsO4)2·2H2O (with M = 13 14 Co, Mg, Mn, Zn, and Cu). The AsO4 stretching region exhibited minor differences between the 15 roselite subgroup minerals, which can be explained by the ionic radius of the cation substituting 16 Peer Review Version 17 on the M position in the structure. Multiple AsO4 antisymmetric stretching and bending modes 18 19 were found, pointing to a tetrahedral symmetry reduction. Bands around 450 cm-–1 were 20 -–1 21 attributed to ν4 bending modes. Several bands in the 300–350 cm region attributed to ν2 22 bending modes also provide evidence of symmetry reduction of the AsO anion. Two broad 23 4 24 bands for roselite were found around 3330 and 3120 cm-–1 and were attributed to the OH 25 26 stretching bands of crystal water. These bands are accompanied by two bands around 1700 and 27 -–1 28 1610 cm attributed to the corresponding OH-bending modes. In conclusion, both XPS and 29 Raman spectroscopy are valuable non-destructive analytical tools to characterize these secondary 30 31 arsenate minerals. X-ray Photoelectron Spectroscopy and Raman microspectroscopy allow the 32 33 chemistry and molecular structure of the roselite group minerals to be studied in a non- 34 destructive way. The minerals in the roselite subgroup are easily distinguished based on their 35 36 chemical composition as determined by XPS. As expected for minerals with the same crystal 37 38 structure, similarities exist in the Raman spectra, sufficient differences exist to be able to identify 39 40 these minerals. 41 Keywords: arsenateArsenate;, roselite group;, roselite;, wendwilsonite;, zincroselite;, brandtite;, 42 43 rruffite;, Raman spectroscopy;, isomorphy 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 2 59 60 Applied Spectroscopy Author Accepted Manuscript Page 4 of 36 1 2 3 4 5 INTRODUCTION 6 7 In nature a wide variety of minerals are known with the general formula X2M(TO4)2.2(H2O) and 8 an important group is formed by minerals with T = As.1 Most of these are found as minor or 9 10 trace minerals in environments such as hydrothermal alterations of primary sulfides and 11 12 arsenides arsenides.2, 3. One of the groups that fit this profile is the roselite group, consisting of 13 14 the minerals roselite, wendwilsonite, zincroselite, brandtite and rruffite, which are all arsenates 15 and the isostructural hydrated sulfate kröhnkite. Within this group in all cases X is Ca, except for 16 Peer Review Version 17 kröhnkite where it is Na, but M can be a variety of metals, e.g. Co, Mg, Mn, Zn, and Cu. 18 19 All minerals in the roselite subgroup crystallize in the monoclinic system with space group 20 21 P21/c. The As atoms are in a regular tetrahedral coordination with four O atoms. The M-site 22 metals are typically divalent and are in an octahedral coordination with four O atoms and two 23 24 (H2O) groups. The Ca atoms are positioned in an irregular [8]-coordinated polyhedron of seven 25 2 26 O atoms and one (H2O) group. The characteristic building block is an infinite chain parallel to 27 the c-axis of octahedral and tetrahedra with composition [M(TO )(H O) ], in which isolated MO 28 4 2 2 6 29 octahedra are connected by corner sharing with TO4 tetrahedra (Fig. 1). This type of chain is 30 31 known as the kröhnkite-type chain, since it was first discovered in kröhnkite.4, 5 32 33 Roselite was originally named in honourhonor of German mineralogist Gustav Rose (18 34 March 18, 1798 Berlin, Germany –15 July 15, 1873 in Berlin, Germany]), Professor of 35 36 Mineralogy, University of Berlin, as an orthorhombic arsenate of lime and . 6. 37 38 Approximately fifty years 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 3 59 60 Applied Spectroscopy Page 5 of 36 Author Accepted Manuscript 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Peer Review Version 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 Figure 1 Crystal structures of roselite, zincroselite, brandtite, wendwilsonite and rruffite 45 46 47 later, Schrauf determined that roselite was not orthorhombic, but had pseudo-orthorhombic 48 49 triclinic elements, that the crystals were lamellar twinned on as many as five of the six elements 50 51 of pseudo-symmetry of the chosen lattice.7-–9 It was Peacock though who finally showed 52 10 53 conclusively that roselite is monoclinic. Roselite has now definitively been determined as 54 belonging to the monoclinic system with point group 2/m (space group P21/c), a = 5.801(1), b = 55 56 57 58 4 59 60 Applied Spectroscopy Author Accepted Manuscript Page 6 of 36 1 2 3 12.898(3), c = 5.617(1), β = 107°42(2)’, Z =2. Crystals tend to be elongated along [100], and] 4 5 and are commonly twinned on {100} with {100} as composition plane.3, 1,11, 1,12 6 7 Wendwilsonite is the Mg-member of the roselite group and exists as a continuous series 8 with roselite. It is pale to intense pink, may even be red and colour zoning is commonly 9 10 observed.3, 1,13 Kolitsch and Fleck 11 reported on the exact crystal structure as part of their 11 12 comprehensive study of minerals and synthetic materials with kröhnkite-type chains. 13 14 Wendwilsonite has a unit cell with a = 5.806(1), b = 12.923(3), c = 5.628(1), β = 107.49(3)°, Z = 15 2., which is slightly different from that reported in the Handbook of Mineralogy 3 and the 16 Peer Review Version 17 original paper by Dunn et al.,13, which reported a = 5.806(1), b = 12.912(2), c = 5.623(2), β = 18 19 107.24(1)°, Z = 2. 20 21 Zincroselite was originally described from the 32 level, sub-level, W 40 stope of the 22 Tsumeb mine (Tsumeb, Oshikoto Region,NamibiaRegion, Namibia) as the Zn -member of the 23 24 roselite group group.14. It forms colourlesscolorless to white aggregates of subparallel crystals up 25 26 to about 1 cm in size. The crystals tend to be prismatic to lath-like and are strongly striated 27 parallel to [001]. Keller et al.14 in their original description reported the unit cell as a = 5.832(2), 28 29 b = 12.889(4), c = 5.644(2), β = 107.72(3)°, Z = 2, but in a more recent publication 15 this was 30 31 adjusted to a = 5.827(1), b = 12.899(3), c = 5.646(1), β = 107.69(3)°, Z = 2 2.15. 32 33 Brandtite is the Mn -analogue of roselite and was named in honourhonor of the Swedish 34 chemist George Brandt (1694-–1768). Wolfe16 originally determined the crystal structure with a 35 36 = 5.65, b = 12.80, c = 5.65 and β = 99°30’. . Recently Herwig and Hawthorne,2, refined the 37 38 crystal structure to a = 5.877(1), b = 12.957(2), c == 5.675(1), β = 108.00°, Z = 2. Brandtite 39 40 occurs as colorless to white, transparent to translucent crystals with a stout to slender prismatic 41 habit with many prism forms visible. Similar to zincroselite it shows striations parallel to [001].1 42 43 In 2011 a new member of the roselite subgroup, the Cu-analogue, was discovered as a 44 45 secondary arsenate in the oxidation zone of the Cu-–As orebody in the Maria Catalina mine, 46 Pampa Larga mining district, Tierra Amarilla, Chile.17 It was named rruffite in honourhonor of 47 48 the RRUFF project, an internet-based database of Raman spectra, X-ray diffraction (XRD), and 49 50 chemical data for minerals. The transparent light blue crystals occurred as granular or blocky 51 52 aggregates and druses. The unit cell is a = 5.8618(2), b = 12.7854(5), c = 5.7025(2) and β = 53 109.42505(2)°. 54 55 56 57 58 5 59 60 Applied Spectroscopy Page 7 of 36 Author Accepted Manuscript 1 2 3 3–- Despite the fact that the oxyanions’ vibrational modes of the oxyanions, such as AsO4 , 4 5 in solutions are relatively well known,18, 1,19, relatively little has been published regarding the 6 20-–22 7 infrared and Raman spectroscopy of the minerals in the roselite group and a systematic 8 study of all the arsenates in this group has never been performed. Ross22 reported for the mid- 9 10 -–1 infrared spectrum of roselite two bands at 985 and 920 cm attributed to the ν1 (AsO4) 11 12 symmetric stretching vibration. The corresponding ν3 antisymmetric stretching vibration as three 13 -–1 -– 14 bands at 870, 850, and 805 cm , while the ν4 bending vibrations were listed at 453 and 435 cm 15 1 1,20 and Frost et al.21 reported Raman data on roselite and wendwilsonite but their spectra and 16 Peer Review Version 17 interpretation is in contradiction with spectra reported by others, such as Yang et al.,17, while 18 19 Frost20 at the same time claimed that the interpretation by Ross22 is not correct. As part of an 20 23-–32 21 ongoing investigation in the spectroscopy of arsenate minerals, this paper aims at reporting 22 for the first time the Raman spectra of all five minerals in the roselite group (roselite, 23 24 wendwilsonite, zincroselite, brandtite, and rruffite) and to address the ambiguities in the 25 26 interpretation of the spectra. 27 28 29 MATERIALS AND METHODS 30 31 Sample originOrigin 32 33 The roselite, wendwilsonite, zincroselite, and brandtite samples were from the author’s private 34 micromount collection, while for rruffite data from the Rruff RRUFF database was used used.33. 35 36 Both the roselite and wendwilsonite were from Bou Azzer, Souss- Massa-Draa, Morocco, the 37 38 zincroselite from Tsumeb, Namibia, and the brandtite from Harstigen Mine, Pajsberg, Filipstad, 39 40 Varmland, Sweden. 41 42 43 X-ray Photoelectron Spectroscopy 44 45 The chemical compositions (Table 1Table I) were determined by using X-ray photoelectron 46 spectroscopy (XPS) on a Kratos AXIS Ultra using a monochromatic Al X-ray source at 225 W 47 48 under ultrahigh vacuum conditions. Each spectral analysis began with a survey scan from 0 to 49 50 1200 eV with a dwell time of 100 milliseconds, pass energy of 160 eV at steps of 1 eV with 1 51 52 sweep. Before analysis, each crystal was etched for 30 minutes to remove surface contamination. 53 54 55 56 57 58 6 59 60 Applied Spectroscopy Author Accepted Manuscript Page 8 of 36 1 2 3 Table 1 Chemical compositions of the minerals used in this study based on XPS survey 4 5 scans (except for Rruffite). 6 7 Chemical formula Ideal formula 8 9 Roselite Ca2.09(Co0.75Mg0.24)Σ0.99(AsO4)2.1.59H2O Ca2Co(AsO4)2.2H2O 10 Wendwilsonite Ca2.01(Mg0.61Co0.35Zn0.02) (AsO4)2·2H2O Ca2Mg(AsO4)2.2H2O 11 Σ=0.96 12 Zincroselite Ca2.04(Zn0.91Mn0.05Mg0.03) Σ=0.99(AsO4)2·2H2O Ca2Zn(AsO4)2.2H2O 13 2+ 14 Brandtite Ca1.99(Mn 0.98Mg0.02)Σ=1.00(AsO4)2·2H2O Ca2Mn(AsO4)2.2H2O 15 * Rruffite Ca2.00Cu1.00(As1.00O4)2 · 2H2O ; Ca2Cu(AsO4)2.2H2O 16 Peer Review Version 17 trace amounts of Fe, S, Al, Mg 18 19 20 21 Raman microscopyMicroscopy 22 The micromount samples were placed on a polished metal surface on the stage of an Olympus 23 24 BHSM microscope equipped with 10x and 50x objectives. The microscope is part of a Renishaw 25 26 1000 Raman microscope system, which also includes a monochromator, a filter system, and a 27 28 charge- coupled device (CCD). Raman spectra were excited by a HeNe laser (633 nm) at a 29 nominal resolution of 2 cm-–1 and collected in the range between 4000 and 100 cm-–1. Repeated 30 31 acquisition using the highest magnification was accumulated to improve the signal to noise ratio. 32 -–1 33 The grating of the Raman microspectrometer was calibrated using the 520.5 cm line of silicon 34 wafer. 35 36 Spectroscopic manipulation, such as baseline adjustment, smoothing, and normalization, 37 38 were was performed using the Fityk 0.9.8 software package,34, which enabled the type of fitting, 39 40 function to be selected, and allows specific parameters to be fixed or varied accordingly. Band 41 fitting was done using a Gauss-–Lorentz cross-product function with the minimum number of 42 43 component bands used for the fitting process. The Gauss- –Lorentz ratio was maintained at 44 45 values greater than 0.7 and fitting was undertaken until reproducible results were obtained with 46 2 47 squared correlations of r greater than 0.995. 48 49 50 RESULTS AND DISCUSSION 51 52 53 * 33. "Rruff, Database of Raman spectroscopy, X-ray diffraction and chemistry of minerals". 54 55 56 57 58 7 59 60 Applied Spectroscopy Page 9 of 36 Author Accepted Manuscript 1 2 3 3-– -–1 The AsO4 anion in solution is characterized by four Raman bands with ν1 at 773 cm , ν2 at 4 5 -–1 -–1 -–1 35 3-– 342 cm , ν3 at 810 cm , and ν4 at 398 cm . The Td symmetry of AsO4 is seldom 6 7 preserved in naturally occurring minerals (Table 2II). 8 9 In recent years there have been several studies on minerals in the roselite subgroup by 10 meansusing of Raman and mid-infrared spectroscopy.17, 2,20, 2,21, 3,33 In the crystal structure of the 11 3-– 12 roselite subgroup minerals the AsO4 group is no longer in the form of a perfect tetrahedron, 13 14 but with a lower symmetry and as a result band splitting can be expected. Associated with 15 3-– 16 changes in the AsO4 symmetry and coordination, the A1 mode may move to different 17 Peer Review Version wavenumbers, while the degenerate E and F modes may split into a number of new A1, B1, 18 19 and/or E modes. The Raman spectra of the minerals in the roselite group between 1050 and 150 20 -–1 21 cm are shown in Fig. 2. 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 Figure 2 Raman spectra of roselite, wendwilsonite, zincroselite, brandtite and rruffite between 53 -1 54 1050 and 180 cm . 55 56 57 58 8 59 60 Applied Spectroscopy Author Accepted Manuscript Page 10 of 36 1 2 3 -–1 The 600 to 1050 cm region (Fig. 3) shows the υ3 antisymmetric stretching and the υ1 4 -–1 5 symmetric stretching modes of the AsO4 -group. The weak band at 709 cm could be due to 6 17 7 H2O libration mode. In all minerals the ν1 symmetric stretching mode was split with a very 8 -–1 9 weak, broad band between 941 and 980 cm and a slightly stronger band between 880 and 909 10 -–1 20 -–1 cm . Frost attributed the band at 976 cm for roselite to the υ1 symmetric stretching 11 12 vibration of PO4 substituting for AsO4. However, no chemical analyses were reported to support 13 14 this. Moreover, the XPS analysis on roselite from the same locality shows no PO4 at all. Finally, 15 16 the band is present in every roselite group mineral (Table 3Table III). Hence, the assignment of 17 Peer Review Version this band to the substitution of a trace of PO4 for AsO4 in the roselite structure is wrong. On the 18 22 -–1 19 other hand, Ross attributed two bands at 985 and 920 cm to the AsO4 υ1 symmetric 20 21 21 stretching mode, which seems more likely to be correct. Interestingly, Frost et al. observed 22 only a single band at 970 cm-–1 for wendwilsonite, while Yang et al.17 reported neither band for 23 24 rruffite, which may be explained by the fact that they did not perform band deconvolution but 25 -–1 26 only reported the major band maxima. The ν3 band shifted from 880 cm for ruffiterruffite (Cu) 27 -–1 -–1 28 to 888 cm for roselite (Co,Mg) and wendwilsonite (Mg,Co) to 889 cm for brandtite (Mn) 29 and to 891 cm-–1 for zincroselite (Zn). 30 17 -–1 31 Yang et al. reported a shift of the ν1 symmetric stretching vibration of 17 cm between 32 33 brandtite (822 cm-–1) and rruffite (832 cm-–1), which they interpreted as being due to the 34 35 substitution of Mn for Cu. Here, the effect of different metal substitutions was also observed, but 36 the single band reported by Yang et al.17 was split into different bands at 846, 839, and 828 cm-– 37 1 38 . Besides the AsO4 symmetry reduction, the observed splitting may be further attributed to the 39 40 presence of multiple metals (Mg, Co, Mn, Zn, and Fe) at the M site in the crystal structure. The 41 antisymmetric stretching mode at 818 cm-–1 for roselite and wendwilsonite were observed at 42 ν3 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 9 59 60 Applied Spectroscopy Page 11 of 36 Author Accepted Manuscript 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Peer Review Version 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 -1 -1 45 Figure 3 Raman spectra in the region between 1000 and 650 cm (to 625 cm for 46 wendwilsonite) showing the υ3 antisymmetric stretching and the υ1 symmetric stretching 47 48 modes of the AsO4-group of roselite, brandtite, zincroselite, wendwilsonite, and rruffite 49 50 (red = original spectrum, black = deconvoluted spectrum). 51 52 53 54 55 56 57 58 10 59 60 Applied Spectroscopy Author Accepted Manuscript Page 12 of 36 1 2 3 Table 3 Comparison and tentative assignment of Raman bands (cm-1) between 1000 and 4 5 160 cm-1 for roselite in comparison to the other members of the roselite group: 6 7 wendwilsonite, brandtite, zincroselite and rruffite. 8 9 Roselite Roselite Wendwilsonite Wendwilsonite Brandtite Zincroselite Rruffite Rruffite 10 This 20 This study 21 This study This study This 17 11 12 study study 13 14 980 976 972 970 (959) (976) (941) - υ 15 16 17 Peer Review Version 18 19 888 909 888 - 889 891 880 - 20 21 865 864 865 871 871 867 865 866 υ 22 23 24 25 26 839 - 840 832 831 847 846 839 υ 27 28 29 30 31 ------839 - 32 33 823 - 827 - 822 827 828 - 34 818 800 818 800 819 808 811 803 35 υ 36 37 38 39 40 787 798 801 - 786 788 799 - 41 - - - - (756) 758 - - 42 43 709 719 709 714 (717) (712) 715 715 υ 44 45 46 47 48 49 50 - 659 667 669 - 656 - - 51 52 53 - 643 - 626 - - - - 54 55 56 57 58 11 59 60 Applied Spectroscopy Page 13 of 36 Author Accepted Manuscript 1 2 3 - 540 550 - - - - - 4 5 6 7 499 - - - - 498 486 485 υ 8 9 10 11 12 475 463 472 478 472 477 479 - υ 13 14 15 16 Peer Review Version 17 450 - 452 454 450 451 450 451 υ 18 19 20 21 22 440 440 448 - 442 - 441 - υ 23 24 25 26 27 425 - 421 425 419 424 426 426 28 υ 29 30 31 32 33 403 399 397 - 401 403 - - 34 377 373 376 - 385 - 382 - υ 35 36 37 38 - - - - 365 - - - 39 40 353 - 356 361 354 353 346 - 41 336 338 339 341 336 336 335 335 υ 42 43 44 45 - - 328 - 312 - 323 - 46 304 307 303 306 297 307 294 294 47 υ 48 49 50 281 264 283 286 279 276 279 - 51 52 241 243 245 244 256 246 249 - 53 - - 238 - 235 - 239 - 54 55 56 57 58 12 59 60 Applied Spectroscopy Author Accepted Manuscript Page 14 of 36 1 2 3 220 211 208 212 218 - - - 4 5 6 7 8 203 197 - 191 204 204 209 - 9 10 188 179 186 164 184 186 184 - 11 12 13 14 15 16 17 Peer Review Version 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 13 59 60 Applied Spectroscopy Page 15 of 36 Author Accepted Manuscript 1 2 3 much lower Raman shifts of 800 cm-–1 by Frost20 and Frost et al.21. Comparable bands were 4 5 found at 819 cm-–1 for brandtite, 808 cm-–1 for zincroselite, and 811 cm-–1 for rruffite. Yang et 6 17 -–1 7 al. observed this band at 803 cm . There is no clear explanation for why these bands were 8 found atlowerat lower Raman shifts by Frost20 and Frost et al.21. In contrast, the antisymmetric 9 ν3 10 20 stretching mode (possible overlapping with the H2O libration mode) was observed for roselite 11 12 and wendwilsonite21 at higher wavenumbers compared to this study (719 vsversus 709 cm-–1 for 13 -–1 14 roselite, 714 vsversus 709 cm for wendwilsonite). 15 20 Frost only described two ν3 antisymmetric stretching modes, a relative intense band at 16 Peer Review Version 17 798 cm-–1 and a weak band at 864 cm-–1. On the other hand, Yang et al. 17 described a very strong 18 19 band at 821 cm-–1, two relative weak bands at 840 and 868 cm-–1 , and a very weak band at 780 20 -–1 21 cm for a sample from the same locality. The sample used in here is from the same locality as 22 those used by Frost20 and Yang et al.17 showing similar bands with different intensities related to 23 24 the orientation of the single crystal under the strongly polarized laser beam.17 Hence, strong 25 26 sharp bands were found at 823 and 839 cm-–1 with a weaker band at 865 cm-–1 and a very weak 27 -–1 17 -–1 28 band at 787 cm . Yang et al. did not deconvolute and the 888 and 818 cm bands were not 29 observed. 30 31 The region below 500 cm-–1 can be split up in roughly 3 three separate sections: 1(i) 400- 32 -–1 - 33 –500 cm covering the υ4 antisymmetric bending modes of the AsO4 -group; 2(ii) 300-–400 cm 34 –1 covering the symmetric bending modes of the AsO -group group; and 3(iii) below 300 cm-– 35 υ2 4 36 1 covering AsO stretching, bending and lattice modes. A relatively sharp band is present at 450 37 38 cm-–1 associated with a number of slightly broader and weaker bands at 475, 440, 425, and 403 39 -–1 40 cm for roselite (Fig. 4), associated with the splitting of the υ4 antisymmetric bending mode of 41 the AsO 3-– group. Frost 20 reported similar bands at 463, 440, and 399 cm-–1, but did not observe 42 4 -–1 -–1 43 the 450 and 425 cm bands. It is uncertain why the ν4 mode at 450 cm , which should be the 44 45 strongest and 46 47 48 49 50 51 52 53 54 55 56 57 58 14 59 60 Applied Spectroscopy Author Accepted Manuscript Page 16 of 36 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Peer Review Version 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 Figure 4 Raman spectra in the region between 525 and 385 cm-1 (from 565 for wendwilsonite) 44 -1 45 showing: 1) 400-500 cm covering the υ4 antisymmetric bending vibrations of the AsO4-group; 46 -1 47 and 2) 300-400 cm covering the υ2 symmetric bending vibrations of the AsO4-group for 48 roselite, brandtite, zincroselite, wendwilsonite, and rruffite (red = original spectrum, black = 49 50 deconvoluted spectrum). 51 52 53 54 55 56 57 58 15 59 60 Applied Spectroscopy Page 17 of 36 Author Accepted Manuscript 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Peer Review Version 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 -1 44 Figure 5 Raman spectra between 385 and 155 to 170 cm covering AsO4 stretching, bending and 45 lattice vibrations for roselite, brandtite, zincrosite, wendwilsonite, and rruffite (red = original 46 47 spectrum, black = deconvoluted spectrum). 48 49 sharpest band in this region for the roselite subgroup minerals, was not detected. Similar bands 50 -–1 51 were found for wendwilsonite at 472, 452, 448, 421, and 397 cm , with comparable bands 52 found at 478, 454, and 419 cm-–1 by Frost et al. 21 while the band at 448 and 397 cm-–1 were 53 54 missing. For brandtite these bands were found at 472, 450, 442, 419, and 401 cm-–1, and for 55 56 zincroselite at 477, 451, 424, and 403 cm-–1, while the band around 440 cm-–1 was not observed. 57 58 16 59 60 Applied Spectroscopy Author Accepted Manuscript Page 18 of 36 1 2 3 For rruffite the bands were found at 479, 451, 441, and 426 cm-–1. The band around 400 cm-–1 4 5 was not detected (Table 2Table II), while Yang et al.17 described only two band maxima at 451 6 -–1 -–1 7 and 426 cm . Similar observations can be made in the 160-–385 cm region for the 8 corresponding AsO symmetric bending modes (Fig. 5). The main sharp band is centered 9 4 υ2 10 around 335-–341 cm-–1. The 160-–300 cm-–1 region consists of a series of bands associated with 11 12 mainly lattice vibrations and AsO stretching and bending vibrations. 13 14 Generally, in the OH-stretching region four separate Raman bands should occur for the 15 two crystal water molecules in the crystal structure. For example, four bands have been observed 16 Peer Review Version 17 for several other arsenate minerals such as annabergite and ,29, 3,31, köttigite, and 18 19 hörnesite.26 The absence of four bands for the roselite subgroup minerals was unexpected. This 20 21 may be caused by accidental degeneracy. The roselite (and other members of the subgroup) unit 22 cell contains two crystallographically different crystal water molecules and hence there should be 23 24 four OH units, which can display both in-phase and out-of-phase vibrations, resulting in four 25 -–1 20 26 possible modes. In the region around 550-–650 cm three bands have been reported by Frost 27 for roselite at 659, 643, and 540 cm-–1 that were attributed to the water libration modes of the 28 29 crystal water (Table 3Table III). These bands were not found in this study, though two bands 30 31 were observed for wendwilsonite at 669 and 626 cm-–1 and single band for zincroselite at 656 32 -–1 33 cm . These bands were not observed for brandtite and rruffite. Since water is a very weak 34 Raman scatterer these bands are expected to be extremely weak and broad, which may be an 35 36 explanation for the observed differences. Harder to explain is the presence of three bands as 37 38 observed by Frost.20. 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 17 59 60 Applied Spectroscopy Page 19 of 36 Author Accepted Manuscript 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Peer Review Version 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Figure 6 Roselite water OH-bending (left) and OH-stretching regions (right) (red = 33 original spectrum, black = deconvoluted spectrum). 34 35 36 37 This is clearly reflected in both the OH-stretching and the OH-bending regions (Table 4Table 38 IV) with both regions characterized by two bands. The OH-stretching region consists of two 39 40 bands centered around 3329 and 3110 cm-–1 for roselite (Fig. 6). Again, it is peculiar that Frost20 41 42 observed three bands in this region for roselite with an extra band 3208 cm-–1 , while at the same 43 44 time observing two OH-bending modes. A similar observation can be made for wendwilsonite, 45 where Frost et al. 21 observed a third band at 3001 cm-–1. No bands were found for rruffite, which 46 47 in this study was due to strong fluorescence at higher Raman shift values. The OH-bending 48 -–1 49 region showed two comparable bands around 1697 and 1593 cm for roselite with comparable 50 bands reported by Frost Frost.20. Similar band positions were found for wendwilsonite, brandtite, 51 52 and zincroselite, though the bands were at slightly higher Raman shifts for wendwilsonite and 53 54 brandtite. No bands were observed for rruffite. 55 56 57 58 18 59 60 Applied Spectroscopy Author Accepted Manuscript Page 20 of 36 1 2 3 Though minor differences in the exact position of the corresponding bands in the other 4 5 minerals of the roselite group were observed there seems to be no direct correlation with the 6 7 presence of Co, Mg, Mn, Zn, or Cu in the crystal structure. The only band that shows a minor 8 effect is the one associated with the antisymmetric stretching vibration of the AsO -group 9 υ3 4 10 around 800-–820 cm-–1 with a shift from 818/815 cm-–1 for roselite/zincroselite (Co and Zn) to 11 12 803 cm-–1 for rruffite (Cu) to 800 cm-–1 for wendwilsonite (Mg), which seems to be associated 13 14 with the ionic radius of the metal from 74 pm for Co and Zn to 73 pm for Cu to 72 pm for Mg. It 15 is unclear why other vibrations are not affected in a similar way and more research is needed to 16 Peer Review Version 17 elucidate the exact effect of the different divalent metals at the M position in the crystal structure 18 19 of the roselite subgroup minerals. 20 21 22 CONCLUSIONS 23 24 X-ray photoelectron spectroscopy (XPS) combined with Raman spectroscopy at room 25 26 temperature has beenwas utilized to characterize the arsenate minerals belonging to the roselite 27 mineral subgroup (roselite, wendwilsonite, brandtite, zincroselite, and rruffite). Extensive 28 29 isomorphic substitution at the M position by Mg, Co, Mn, and Cu has been found. None of the 30 31 minerals have been determined to be complete endmembers, except for rruffite. The observed 32 33 vibrational modes of the Raman spectra have been interpreted in relation to the crystal structure 34 of the roselite subgroup minerals. These minerals can be described by the typical vibrational 35 -–1 36 modes of the AsO4 units. The ν1 symmetric stretching modes occur in the regions 880-–980 cm 37 -–1 38 and 840–870 cm region. The ν3 antisymmetric stretching modes occur in the regions 865-–871 39 -–1 -–1 -–1 40 cm and 803–818 cm region. Several bands found around 780 cm region are assigned to 41 -–1 water librational modes. The ν4 ν4 bending modes occur in the region 464-–479 cm and the ν2 42 43 bending modes in the region 294–361 cm-–1 region. Multiple bands are found in the above- 44 45 mentioned regions point to a lowering of the symmetry of the AsO4 unit from the ideal 46 47 tetrahedral symmetry Td. Crystal water was observed as two bands in both the OH-stretching 48 region (around 3330 and 3120 cm-–1) and OH-bending region (around 1680-–1724 cm-–1 and 49 50 1593-–1629 cm-–1). 51 52 53 ACKNOWLEDGMENTS 54 55 56 57 58 19 59 60 Applied Spectroscopy Page 21 of 36 Author Accepted Manuscript 1 2 3 The author thanks the School of Chemistry, Physics and Mechanical Engineering, Science and 4 5 Engineering Faculty, Queensland University of Technology for the use of their instrumentation. 6 7 The author thanks Dr. Barry Wood for his valuable help with the XPS analyses. The author 8 acknowledges the facilities, and the scientific and technical assistance, of the Australian 9 10 Microscopy & Microanalysis Research Facility at the Centre for Microscopy and Microanalysis, 11 12 The University of Queensland. 13 14 15 DECLARATION OF CONFLICTING INTERESTS 16 Peer Review Version 17 The Author declares that there is no conflict of interest 18 19 20 21 REFERENCES 22 23 24 1. R.V. Gaines, H.C.W. Skinner, E.E. Foord, B. Mason, A. Rosenzweig. Dana's New 25 26 Mineralogy: The System of Mineralogy of James Dwight Dana and Edward Salisbury 27 Dana. New York: John Wiley and Sons, Inc., 1997. 28 29 2. S. Herwig, F.C. Hawthorne. "The Topology of Hydrogen Bonding in Brandtite, Collinsite, and 30 31 Fairfieldite". Can. Mineral. 2006. 44(5): 1181–1196. 32 33 3. J.W. Anthony, R.A. Bideaux, K.W. Bladh, M.C. Nichols. Handbook of Mineralogy Volume 34 IV: Arsenates, Phosphates and Vanadates. Tuscon, Arizona: Mineral Data Publishing, 35 36 2000. 37 38 4. B. Dahlman. "The Crystal Structures of Kröhnkite, CuNa2(SO4)2.2H2O, and Brandtite, 39 40 MnCa2(AsO4)2.2H2O". Arkiv Min. Geol. 1952. 1: 339–366. 41 5. F.C. Hawthorne, R.B. Ferguson. "Refinement of the Crystal Structure of Kröhnkite". Acta 42 43 Crystallogr. 1975. B31(6): 1753–1755. 44 45 6. A. Lévy. "Account of a New Mineral Substance". Annals Phil. 1874. 24(6): 439–442. 46 7. A. Schrauf. "Roselite". Jahrb. Min. 1874. 868. 47 48 8. A. Schrauf. "Zur Charakteristik der Mineralspecies Roselit". Tschermak's Mineral. Mitt. 1873. 49 50 291–293. 51 52 9. A. Schrauf. "Monographie des Roselith". Tschermak's Mineral. Mitt. 1874. 137–160. 53 10. M.A. Peacock. "Roselite and the Rule of Highest Pseudosymmetry". Am. Mineral. 1936. 54 55 21(9): 589–603. 56 57 58 20 59 60 Applied Spectroscopy Author Accepted Manuscript Page 22 of 36 1 2 3 11. U. Kolitsch, M. Fleck. "Third Update on Compounds with Krohnkite-Type Chains: The 4 5 Crystal Structure of Wendwilsonite [Ca2Mg(AsO4)2·2H2O] and the New Triclinic 6 7 Structure Types of Synthetic AgSc(CrO4)2·2H2O and M2Cu(Cr2O7)2·2H2O (M = Rb, Cs)". 8 Eur. J. Mineral. 2006. 18(4) 471–482. 9 10 12. F.C. Hawthorne, R.B. Ferguson. "The Crystal Structure of Roselite". Can. Mineral. 1977. 11 12 15(Pt. 1): 36–42. 13 14 13. P.J. Dunn, B.D. Sturman, J.A. Nelen. "Wendwilsonite, the Magnesium Analogue of Roselite, 15 from Morocco, New Jersey, and Mexico, and New Data on Roselite". Am. Mineral. 16 Peer Review Version 17 1987. 72(1–2): 217–221. 18 19 14. P. Keller, J. Innes, P.J. Dunn. "Zincroselite, Ca2Zn(AsO4)2·2H2O, a New Mineral from 20 21 Tsumeb, Namibia". Neues Jahrb. Mineral., Monatsh. 1986. 1986(11): 523–527. 22 15. P. Keller, F. Lissner, T. Schleid. "The Crystal Structures of Zincroselite and Gaitite: Two 23 24 Natural Polymorphs of Ca2Zn(AsO4)2·2H2O from Tsumeb, Namibia". Eur. J. Mineral. 25 26 2004. 16(2): 353–359. 27 16. C.W. Wolfe. "Classification of Minerals of the Type A (XO ) .nH O". Am. Mineral. 1940. 28 3 4 2 2 29 25(11): 738–754, 787–809. 30 31 17. H. Yang, R.A. Jenkins, R.T. Downs, S.H. Evans. "Rruffite, Ca2Zn(AsO4)2·2H2O, a New 32 33 Member of the Roselite Group, from Tierra Amarilla, Chile". Can. Mineral. 2011. 49(3): 34 877–884. 35 36 18. F.K. Vansant, B.J. van der Veken, H.O. Desseyn. "Vibrational Analysis of Arsenic Acid and 37 38 its Anions. I. Description of the Raman Spectra". J. Mol. Struct. 1973. 15(3): 425–437. 39 40 19. S.C.B. Myneni, S.J. Traina, G.A. Waychunas, T.J. Logan. "Experimental and Theoretical 41 Vibrational Spectroscopic Evaluation of Arsenate Coordination in Aqueous Solutions, 42 43 Solids, and at Mineral–Water Interfaces". Geochim. Cosmochim. Acta. 1998. 62(19/20): 44 45 3285–3300. 46 20. R.L. Frost. "Raman and Infrared Spectroscopy of Arsenates of the Roselite and Fairfieldite 47 48 Mineral Subgroups". Spectrochim. Acta, Part A. 2009. 71A(5): 1788–1794. 49 50 21. R.L. Frost, R. Scholz, A. Lopez, F.M. Belotti, Y. Xi. "Structural Characterization and 51 52 Vibrational Spectroscopy of the Arsenate Mineral Wendwilsonite". Spectrochim. Acta, 53 Part A. 2014. 118: 737–743. 54 55 56 57 58 21 59 60 Applied Spectroscopy Page 23 of 36 Author Accepted Manuscript 1 2 3 22. S. D. Ross, "Phosphates and Other Oxy-Anions of Group V". In: V.C. Farmer, editor. The 4 5 Infrared Spectra of Minerals. London: Mineralogical Society, 1974. Pp. 383–422. 6 7 23. R.L. Frost, J.T. Kloprogge. "Raman Spectroscopy of Some Complex Arsenate Minerals – 8 Implications for Soil Remediation". Spectrochim. Acta, Part A. 2003. 59(12): 2797– 9 10 2804. 11 12 24. R.L. Frost, J.T. Kloprogge, W.N. Martens. "Raman Spectroscopy of the Arsenates and 13 14 Sulphates of the Mineral Group". J. Raman Spectrosc. 2004. 35(1): 28–35. 15 25. R.L. Frost, J.T. Kloprogge, M. L. Weier, W.N. Martens, et al. "Raman Spectroscopy of 16 Peer Review Version 17 Selected Arsenates: Implications for Soil Remediation". Spectrochim. Acta, Part A. 2003. 18 19 59(10): 2241–2246. 20 21 26. R.L. Frost, W.N. Martens, P.A. Williams, J.T. Kloprogge. "Raman Spectroscopic Study of 22 the Vivianite Arsenate Minerals". J. Raman Spectrosc. 2003. 34(10): 751–759. 23 24 27. J.T. Kloprogge, R.L. Frost. "Raman Microscopy Study of Cafarsite". Appl. Spectrosc. 1999. 25 26 53(7): 874–880. 27 28. J.T. Kloprogge, R.L. Frost. "A Raman Microscopy Study of Tyrolite: A Multi-Anion 28 29 Arsenate Mineral". Appl. Spectrosc. 2000. 54(4): 517–521. 30 31 29. W.N. Martens, R.L. Frost, J.T. Kloprogge. "Raman Spectroscopy of Synthetic Erythrite, 32 33 Partially Dehydrated Erythrite and Hydrothermally Synthesized Dehydrated Erythrite". J. 34 Raman Spectrosc. 2003. 34(1): 90–95. 35 36 30. W.N. Martens, R.L. Frost, J.T. Kloprogge, P.A. Williams. "The Basic Copper Arsenate 37 38 Minerals Olivenite, , , and Clinoclase: An Infrared Emission and 39 40 Raman Spectroscopic Study". Am. Mineral. 2003. 88(4): 501–508. 41 31. W.N. Martens, J.T. Kloprogge, R.L. Frost, L. Rintoul. "Site Occupancy of Co and Ni in 42 43 Erythrite–Annabergite Solid Solutions Deduced by Vibrational Spectroscopy". Can. 44 45 Mineral. 2005. 43(3): 1065–1075. 46 32. W.N. Martens, J.T. Kloprogge, R.L. Frost, L. Rintoul. "Single-Crystal Raman Study of 47 48 Erythrite, Co3(AsO4)2.8H2O". J. Raman Spectrosc. 2004. 35(3): 208–216. 49 50 33. RRUF Project. "Rruff: Database of Raman Spectroscopy, X-ray Diffraction and Chemistry of 51 52 Minerals". http://rruff.info/ [accessed Dec 6, 2020]. 53 34. M. Wojdyr. "Fityk: A General-Purpose Peak Fitting Program". J. Appl. Crystallogr. 2010. 54 55 43(5–1): 1126–1128. 56 57 58 22 59 60 Applied Spectroscopy Author Accepted Manuscript Page 24 of 36 1 2 3 35. S.D. Ross. Inorganic Infrared and Raman Spectra. Maidenhead: McGraw-Hill, 1972. 4 5 1. R. V. Gaines, H. C. W. Skinner, E. E. Foord, B. Mason, and A. Rosenzweig, Dana's New 6 7 Mineralogy - The System of Mineralogy of James Dwight Dana and Edward Salisbury 8 Dana, Eighth Edition. New York: John Wiley & Sons, Inc., 1997. 9 10 2. S. Herwig and F. C. Hawthorne."The Topology of Hydrogen Bonding in Brandtite, 11 12 Collinsite, and Fairfieldite", Can. Mineral. 2006. 44(5): 1181-1196. 13 14 3. J. W. Anthony, R. A. Bideaux, K. W. Bladh, and M. C. Nichols, Handbook of 15 Mineralogy Volume IV - Arsenates, Phosphates and Vanadates. Tuscon, Arizona, USA: 16 Peer Review Version 17 Mineral Data Publishing, 2000. 18 19 4. B. Dahlman."The Crystal Structures of Kröhnkite, CuNa2(SO4)2.2H2O, and Brandtite, 20 21 MnCa2(AsO4)2.2H2O", Arkiv Min. Geol. 1952. 1: 339-366. 22 5. F. C. Hawthorne and R. B. Ferguson."Refinement of the Crystal Structure of Kröhnkite", 23 24 Acta Crystallogr. 1975. B31(6): 1753-1755. 25 26 6. A. Lévy."Account of a New Mineral Substance", Annals Phil. 1874. 24(6): 439-442. 27 7. A. Schrauf."Roselite", Jahrb. Min. 1874. 868. 28 29 8. A. Schrauf."Zur Charakteristik der Mineralspecies Roselit", Tschermak's Mineral. Mitt. 30 31 1873. 291-293. 32 33 9. A. Schrauf."Monographie des Roselith", Tschermak's Mineral. Mitt. 1874. 137-160. 34 10. M. A. Peacock."Roselite and the Rule of Highest Pseudosymmetry", Am. Mineral. 1936. 35 36 21(9): 589-603. 37 38 11. U. Kolitsch and M. Fleck."Third Update on Compounds with Krohnkite-Type Chains: 39 40 the Crystal Structure of Wendwilsonite [Ca2Mg(AsO4)2·2H2O] and the New Triclinic 41 Structure Types of Synthetic AgSc(CrO4)2·2H2O and M2Cu(Cr2O7)2·2H2O (M = Rb, 42 43 Cs)", Eur. J. Mineral. 2006. 18(4) 471-482. 44 45 12. F. C. Hawthorne and R. B. Ferguson."The Crystal Structure of Roselite", Can. Mineral. 46 1977. 15(Pt. 1): 36-42. 47 48 13. P. J. Dunn, B. D. Sturman, and J. A. Nelen."Wendwilsonite, the Magnesium Analogue of 49 50 Roselite, from Morocco, New Jersey, and Mexico, and New Data on Roselite", Am. 51 52 Mineral. 1987. 72(1-2): 217-221. 53 14. P. Keller, J. Innes, and P. J. Dunn."Zincroselite, Ca Zn(AsO ) ·2H O, a New Mineral 54 2 4 2 2 55 from Tsumeb, Namibia", Neues Jahrb. Mineral., Monatsh. 1986. 1986(11): 523-527. 56 57 58 23 59 60 Applied Spectroscopy Page 25 of 36 Author Accepted Manuscript 1 2 3 15. P. Keller, F. Lissner, and T. Schleid."The Crystal Structures of Zincroselite and Gaitite: 4 5 Two Natural Polymorphs of Ca2Zn[AsO4]2·2H2O from Tsumeb, Namibia", Eur. J. 6 7 Mineral. 2004. 16(2): 353-359. 8 16. C. W. Wolfe."Classification of Minerals of the Type A (XO ) .nH O", Am. Mineral. 9 3 4 2 2 10 1940. 25(11): 738-754,787-809. 11 12 17. H. Yang, R. A. Jenkins, R. T. Downs, and S. H. Evans."Rruffite, Ca2Cu(AsO4)2.2H2O, a 13 14 New Member of the Roselite Group, from Tierra Amarilla, Chile", Can. Mineral. 2011. 15 49(3): 877-884. 16 Peer Review Version 17 18. F. K. Vansant, B. J. van der Veken, and H. O. Desseyn."Vibrational Analysis of Arsenic 18 19 Acid and its Anions. I. Description of the Raman Spectra", J. Mol. Struct. 1973. 15(3): 20 21 425-437. 22 19. S. C. B. Myneni, S. J. Traina, G. A. Waychunas, and T. J. Logan."Experimental and 23 24 Theoretical Vibrational Spectroscopic Evaluation of Arsenate Coordination in Aqueous 25 26 Solutions, Solids, and at Mineral-Water Interfaces", Geochim. Cosmochim. Acta. 1998. 27 62(19/20): 3285-3300. 28 29 20. R. L. Frost."Raman and Infrared Spectroscopy of Arsenates of the Roselite and 30 31 Fairfieldite Mineral Subgroups", Spectrochim. Acta A. 2009. 71A(5): 1788-1794. 32 33 21. R. L. Frost, R. Scholz, A. Lopez, F. M. Belotti, and Y. Xi."Structural Characterization 34 and Vibrational Spectroscopy of the Arsenate Mineral Wendwilsonite", Spectrochim. 35 36 Acta A. 2014. 118: 737-743. 37 38 22. S. D. Ross, "Phosphates and Other Oxy-Anions of Group V", in: V. C. Farmer, editor. 39 40 The Infrared Spectra of Minerals. London: Mineralogical Society, 1974. 383-422. 41 23. R. L. Frost and J. T. Kloprogge."Raman Spectroscopy of Some Complex Arsenate 42 43 Minerals – Implications for Soil Remediation", Spectrochim. Acta A. 2003. 59(12): 44 45 2797-2804. 46 24. R. L. Frost, J. T. Kloprogge, and W. N. Martens."Raman Spectroscopy of the Arsenates 47 48 and Sulphates of the Tsumcorite Mineral Group", J. Raman Spectrosc. 2004. 35(1): 28- 49 50 35. 51 52 25. R. L. Frost, J. T. Kloprogge, M. L. Weier, W. N. Martens, Z. Ding, and H. G. H. 53 Edwards."Raman Spectroscopy of Selected Arsenates – Implications for Soil 54 55 Remediation", Spectrochim. Acta A. 2003. 59(10): 2241-2246. 56 57 58 24 59 60 Applied Spectroscopy Author Accepted Manuscript Page 26 of 36 1 2 3 26. R. L. Frost, W. N. Martens, P. A. Williams, and J. T. Kloprogge."Raman Spectroscopic 4 5 Study of the Vivianite Arsenate Minerals", J. Raman Spectrosc. 2003. 34(10): 751-759. 6 7 27. J. T. Kloprogge and R. L. Frost."Raman Microscopy Study of Cafarsite", Appl. 8 Spectrosc. 1999. 53(7): 874-880. 9 10 28. J. T. Kloprogge and R. L. Frost."A Raman Microscopy Study of Tyrolite; a Multi-anion 11 12 Arsenate Mineral", Appl. Spectrosc. 2000. 54(4): 517-521. 13 14 29. W. N. Martens, R. L. Frost, and J. T. Kloprogge."Raman Spectroscopy of Synthetic 15 Erythrite, Partially Dehydrated Erythrite and Hydrothermally Synthesized Dehydrated 16 Peer Review Version 17 Erythrite", J. Raman Spectrosc. 2003. 34(1): 90-95. 18 19 30. W. N. Martens, R. L. Frost, J. T. Kloprogge, and P. A. Williams."The Basic Copper 20 21 Arsenate Minerals Olivenite, Cornubite, Cornwallite, and Clinoclase: an Infrared 22 Emission and Raman Spectroscopic Study", Am. Mineral. 2003. 88(4): 501-508. 23 24 31. W. N. Martens, J. T. Kloprogge, R. L. Frost, and L. Rintoul."Site Occupancy of Co and 25 26 Ni in Erythrite-Annabergite Solid Solutions Deduced by Vibrational Spectroscopy", Can. 27 Mineral. 2005. 43(3): 1065-1075. 28 29 32. W. N. Martens, J. T. Kloprogge, R. L. Frost, and L. Rintoul."Single-Crystal Raman Study 30 31 of Erythrite, Co3(AsO4)2.8H2O", J. Raman Spectrosc. 2004. 35(3): 208-216. 32 33 33. "Rruff, Database of Raman spectroscopy, X-ray diffraction and chemistry of minerals". 34 http://rruff.info/. 35 36 34. M. Wojdyr."Fityk: a General-Purpose Peak Fitting Program", J. Appl. Crystallogr. 2010. 37 38 43(5-1): 1126-1128. 39 40 35. S. D. Ross, Inorganic Infrared and Raman Spectra. Maidenhead: McGraw-Hill, 1972. 41 42 43 Captions 44 45 Figure 1. Crystal structures of roselite, zincroselite, brandtite, wendwilsonite, and rruffite. 46 47 48 Figure 2. Raman spectra of roselite, wendwilsonite, zincroselite, brandtite and rruffite between 49 50 1050 and 180 cm–1. 51 52 53 Figure 3. Raman spectra in the region between 1000 and 650 cm–1 (to 625 cm–1 for 54 55 wendwilsonite) showing the υ3 antisymmetric stretching and the υ1 symmetric stretching modes 56 57 58 25 59 60 Applied Spectroscopy Page 27 of 36 Author Accepted Manuscript 1 2 3 of the AsO4 group of roselite, brandtite, zincroselite, wendwilsonite, and rruffite (red = original 4 5 spectrum, black = deconvoluted spectrum). 6 7 8 Figure 4. Raman spectra in the region between 525 and 385 cm–1 (from 565 for wendwilsonite) 9 10 –1 showing: (1) 400–500 cm covering the υ4 antisymmetric bending vibrations of the AsO4 group; 11 –1 12 and (2) 300–400 cm covering the υ2 symmetric bending vibrations of the AsO4 group for 13 14 roselite, brandtite, zincroselite, wendwilsonite, and rruffite (red = original spectrum, black = 15 deconvoluted spectrum). 16 17 Peer Review Version 18 –1 19 Figure 5. Raman spectra between 385 and 155 to 170 cm covering AsO4 stretching, bending 20 21 and lattice vibrations for roselite, brandtite, zincrosite, wendwilsonite, and rruffite (red = original 22 spectrum, black = deconvoluted spectrum). 23 24 25 26 Figure 6. Roselite water OH-bending (left) and OH-stretching regions (right) (red = original 27 spectrum, black = deconvoluted spectrum). 28 29 30 31 Tables 32 33 Table I. Chemical compositions of the minerals used in this study based on XPS survey 34 scans (except for Rruffite). 35 36 Mineral Chemical formula Ideal formula 37 38 Roselite Ca2.09(Co0.75Mg0.24)Σ0.99(AsO4)2.1.59H2O Ca2Co(AsO4)2.2H2O 39 40 Wendwilsonite Ca2.01(Mg0.61Co0.35Zn0.02)Σ=0.96(AsO4)2·2H2O Ca2Mg(AsO4)2.2H2O 41 Zincroselite Ca (Zn Mn Mg ) (AsO ) ·2H O Ca Zn(AsO ) .2H O 42 2.04 0.91 0.05 0.03 Σ=0.99 4 2 2 2 4 2 2 2+ 43 Brandtite Ca1.99(Mn 0.98Mg0.02)Σ=1.00(AsO4)2·2H2O Ca2Mn(AsO4)2.2H2O 44 33 45 Rruffite Ca2.00Cu1.00(As1.00O4)2 · 2H2O ; Ca2Cu(AsO4)2.2H2O 46 47 trace amounts of Fe, S, Al, Mg 48 49 3– 50 Table II. Normal modes of AsO4 in different symmetries. 51 52 Normal modes 53 54 Symmetry ν1 ν2 ν3 ν4 55 Td A1 E F2 F2 56 57 58 26 59 60 Applied Spectroscopy Author Accepted Manuscript Page 28 of 36 1 2 3 C3v A1 E A1 + E A1 +E 4 5 C2v A1 A1 + A2 A1 + B1 + B2 A1 + B1 + B2 6 7 C1 A 2A 3A 3A 8 9 10 Table III. Comparison and tentative assignment of Raman bands (cm–1) between 1000 and 11 12 160 cm–1 for roselite in comparison to the other members of the roselite group: 13 14 wendwilsonite, brandtite, zincroselite and rruffite. 15 Roselite Roselite Wendwilsonite Wendwilsonite Brandtite Zincroselite Rruffite Rruffite 16 Peer Review Version 17 This 20 This study 21 This study This study This 17 18 19 study study 20 21 980 976 972 970 (959) (976) (941) – υ 22 23 24 25 26 888 909 888 – 889 891 880 – 27 28 865 864 865 871 871 867 865 866 υ 29 30 31 32 33 839 – 840 832 831 847 846 839 υ 34 35 36 37 38 – – – – – – 839 – 39 40 823 – 827 – 822 827 828 – 41 818 800 818 800 819 808 811 803 υ 42 43 44 45 46 47 787 798 801 – 786 788 799 – 48 – – – – (756) 758 – – 49 50 709 719 709 714 (717) (712) 715 715 υ 51 52 53 54 55 56 57 58 27 59 60 Applied Spectroscopy Page 29 of 36 Author Accepted Manuscript 1 2 3 – 659 667 669 – 656 – – 4 5 6 7 – 643 – 626 – – – – 8 9 10 – 540 550 – – – – – 11 12 13 14 499 – – – – 498 486 485 υ 15 16 17 Peer Review Version 18 19 475 463 472 478 472 477 479 – υ 20 21 22 23 24 450 – 452 454 450 451 450 451 υ 25 26 27 28 29 440 440 448 – 442 – 441 – υ 30 31 32 33 34 425 – 421 425 419 424 426 426 υ 35 36 37 38 39 40 403 399 397 – 401 403 – – 41 377 373 376 – 385 – 382 – υ 42 43 44 45 – – – – 365 – – – 46 353 – 356 361 354 353 346 – 47 48 336 338 339 341 336 336 335 335 υ 49 50 51 52 – – 328 – 312 – 323 – 53 304 307 303 306 297 307 294 294 υ 54 55 56 57 58 28 59 60 Applied Spectroscopy Author Accepted Manuscript Page 30 of 36 1 2 3 281 264 283 286 279 276 279 – 4 5 241 243 245 244 256 246 249 – 6 7 – – 238 – 235 – 239 – 8 220 211 208 212 218 – – – 9 10 11 12 13 14 203 197 – 191 204 204 209 – 15 188 179 186 164 184 186 184 – 16 17 Peer Review Version 18 19 20 21 Table IV. Comparison of the OH stretching and bending modes of water in roselite, 22 wendwilsonite, brandtite, zincroselite and rruffite. 23 24 Roseli Roseli Wendwilso Wendwilso Brandti Zincrosel Rruffi Rruffi Assignm 25 26 te te 20 nite nite te ite te te 17 ent 27 21 28 This This study This This This 29 study study33 study3333 study 30 31 33 32 33 3329 3450 3331 3332 3309 3426 – – OH- 34 stretch 35 36 water 37 38 – 3208 – – – – – 39 40 3110 3121 3122 3119 3058 3338 – – 41 – 3042 – 3001 – – – – 42 43 1697 1688 1683 1724 1713 1691 – – OH-bend 44 45 water 46 47 1593 1611 1595 1624 1629 1614 – – 48 49 50 51 52 53 54 55 56 57 58 29 59 60 Applied Spectroscopy Page 31 of 36 Author Accepted Manuscript 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Peer Review Version 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 Figure 1 Crystal structures of roselite, zincroselite, brandtite, wendwilsonite and rruffite 41 42 177x185mm (300 x 300 DPI) 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Applied Spectroscopy Author Accepted Manuscript Page 32 of 36 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Peer Review Version 18 19 20 21 22 23 24 25 26 27 28 Figure 2 Raman spectra of roselite, wendwilsonite, zincroselite, brandtite and rruffite between 1050 and 180 29 cm-1. 30 177x116mm (150 x 150 DPI) 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Applied Spectroscopy Page 33 of 36 Author Accepted Manuscript 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Peer Review Version 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 Figure 3 Raman spectra in the region between 1000 and 650 cm-1 (to 625 cm-1 for wendwilsonite) showing 41 the υ3 antisymmetric stretching and the υ1 symmetric stretching modes of the AsO4-group of roselite, 42 brandtite, zincroselite, wendwilsonite, and rruffite (red = original spectrum, black = deconvoluted spectrum). 43 44 177x185mm (300 x 300 DPI) 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Applied Spectroscopy Author Accepted Manuscript Page 34 of 36 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Peer Review Version 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 Figure 4 Raman spectra in the region between 525 and 385 cm-1 (from 565 for wendwilsonite) showing: 1) 40 400-500 cm-1 covering the υ4 antisymmetric bending vibrations of the AsO4-group; and 2) 300-400 cm-1 41 covering the υ2 symmetric bending vibrations of the AsO4-group for roselite, brandtite, zincroselite, 42 wendwilsonite, and rruffite (red = original spectrum, black = deconvoluted spectrum). 43 44 177x181mm (300 x 300 DPI) 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Applied Spectroscopy Page 35 of 36 Author Accepted Manuscript 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Peer Review Version 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 Figure 5 Raman spectra between 385 and 155 to 170 cm-1 covering AsO4 stretching, bending and lattice 40 vibrations for roselite, brandtite, zincrosite, wendwilsonite, and rruffite (red = original spectrum, black = 41 deconvoluted spectrum). 42 43 177x181mm (300 x 300 DPI) 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Applied Spectroscopy Author Accepted Manuscript Page 36 of 36 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Peer Review Version 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 Figure 6 Roselite water OH-bending (left) and OH-stretching regions (right) (red = original spectrum, black 46 = deconvoluted spectrum). 47 88x116mm (300 x 300 DPI) 48 49 50 51 52 53 54 55 56 57 58 59 60 Applied Spectroscopy Page 37 of 36 Author Accepted Manuscript 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Peer Review Version 18 19 20 21 22 1098x439mm (96 x 96 DPI) 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Applied Spectroscopy