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Frost, Ray L. and Bahfenne, Silmarilly (2010) Raman spectroscopic study of the antimonate lewisite (Ca,Fe,Na)2(Sb,Ti)2O6(O,OH)7. Radiation Effects and Defects in Solids, 165(1). pp. 46-53.

© Copyright 2010 Taylor and Francis

1 Raman spectroscopic study of the antimonate mineral lewisite

2 (Ca,Fe,Na)2(Sb,Ti)2O6(O,OH)7 3 4 Silmarilly Bahfenne and Ray L. Frost  5 6 Inorganic Materials Research Program, School of Physical and Chemical Sciences, 7 Queensland University of Technology, GPO Box 2434, Brisbane Queensland 4001, 8 . 9 10 11 Corresponding Author: [email protected] 12 P +61 7 3138 2407 13 F: +61 7 3138 1804

 Author to whom correspondence should be addressed ([email protected]) 1

14 Raman spectroscopic study of the antimonate mineral lewisite

15 (Ca,Fe,Na)2(Sb,Ti)2O6(O,OH)7 16 17 18 19 Abstract 20

21 The mineral lewisite, (Ca,Fe,Na)2(Sb,Ti)2O6(O,OH)7 an bearing mineral has been 22 studied by Raman spectroscopy. A comparison is made with the Raman spectra of other 23 including bindheimite, stibiconite and roméite. The mineral lewisite is characterised 24 by an intense sharp band at 517 cm-1 with a shoulder at 507 cm-1 assigned to SbO stretching 25 modes. Raman bands of medium intensity for lewisite are observed at 300, 356 and 400 26 cm-1. These bands are attributed to OSbO bending vibrations. 27 Raman bands in the OH stretching region are observed at 3200, 3328, 3471 cm-1 with a 28 distinct shoulder at 3542 cm-1. The latter is assigned to the stretching vibration of OH units. 29 The first three bands are attributed to water stretching vibrations. The observation of bands in 30 the 3200 to 3500 cm-1 region suggests that water is involved in the lewisite structure. If this is 2+ 31 the case then the formula may be better written as Ca, Fe , Na)2(Sb, Ti)2(O,OH)7 ·xH2O. 32 33 Keywords: antimonate, lewisite, bindheimite, bahianite, Raman Spectroscopy, 34 35 1. Introduction 36

37 There are a group of minerals based upon the formula (A)2 (X2O6) (O,OH,F) of which

38 the mineral lewisite (Ca,Fe,Na)2(Sb,Ti)2O6(O,OH)7 is one. Table 1 lists these minerals of the 39 stibiconite group, their formula, and space group. These minerals include 3+ 5+ 40 many common antimony bearing minerals such as stibiconite Sb Sb 2O6(OH), bindheimite 2+ 41 Pb2Sb2O6(O,OH) and lewisite (Ca, Fe , Na)2(Sb, Ti)2O7. The mineral has been more closely 2+ 42 related to the antimony mineral roméite (Ca, Fe , Mn, Na)2(Sb, Ti)2O6(O, OH, F) . However 43 this may not be correct (1). The of lewisite has been solved (2). The crystal 44 structure of lewisite, is cubic, space group Fd3m, a = 10.311(7) Ã, Z = 8. The - 45 like structure contains distorted A cubes and B octahedra. A comparison among lewisite and 46 several other pyrochlore-like structures with B=Sb5+ shows that increase of the unit cell

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47 parameter depends on the size of the A-cations. Further refinement has been undertaken by 48 Rouse et al. (1). 49 50 It is interesting to note that only very few papers have been published on the 51 spectroscopy of minerals containing antimony (3). What research has been published is 52 related to the analysis of pigments (4-6). Some spectroscopic analyses of and lead 53 antimonates have been forthcoming (7-9). Very few studies of related minerals such as 54 natural antimonates have been undertaken (10-12). In some studies of antimonite containing 55 minerals, it was found that the hydroxyl unit was coordinated directly to the metal ion and 56 formed hydrogen bonds with the antimonate anion (13). Raman spectroscopy has proven 57 especially useful for the study of related minerals. As part of a comprehensive study of the 58 molecular structure of secondary minerals containing oxy-anions, formed in the oxide zone, 59 using IR and Raman spectroscopy, we report the Raman properties of the antimonate mineral 60 lewisite. 61 62 The aim of this paper is to report the Raman spectra of lewisite and related minerals 63 of the stibiconite group and to relate the spectra to its crystal chemistry. The paper follows 64 the systematic research on Raman and infrared spectroscopy of secondary minerals 65 containing oxy-anions formed in oxidation zone. 66 67 2. Experimental 68 69 2.1 Minerals 70 71 The mineral bindheimite was obtained on loan from The South Australian Museum. 72 The mineral originated from Tripuhy, . The chemical analysis of this mineral has been 73 published by Anthony et al. (page 313) (14). The mineral analysed as FeO 4.55%, MnO

74 0.38%, CaO 15.93 %, Na2O 0.99%, TiO2 11.35%, Sb2O3 67.5%. A spectrum of lewisite may 75 be found in the RRUFF data base for comparison. The stibiconite mineral was obtained from 76 Museum South Australia and originated from the Yucunani Mine, Tejocotes, Oaxaca, 77 Mexico. The composition of this mineral has been published (15). In the work of Vitaliano 78 and Mason the analyses of some 33 samples of stibiconite were presented (16). These authors 79 showed that Ca was always present in the structure and also water was present in the 80 structure. The mineral bindheimite was obtained on loan from The South Australian 3

81 Museum. The origin of the mineral is the Wamsley Mine, Mineral County, Nevada, USA. 82 The chemical analysis of this mineral has been published (14). 83

84 The mineral roméite Ca2Sb2O6(OH,F,O) was supplied by The South Australian Museum and 85 originated from Starlera valley, Switzerland. The composition of the mineral has been 86 published (15). The mineral is found in a wide range of sites world wide (15). The origin of 87 the minerals was from (a) Praborna Mine, Aosta Valley, St. Marcel, and (b) Le Cetina, 88 Cotomiano, Siena Province, Tuscany, Italy. The analysis of the Praborna Mine roméite is 89 given on page 479 by Anthony et al. (15). Roméite functions as tourmalines as a catch-all for 90 excess cations such as Fe, Mn, Zn, Ti, Si and, especially, for large cations such as Pb, Na, and 91 K. 92 93 2.2 Raman spectroscopy 94 95 The crystals of the antimony bearing minerals were placed and oriented on the stage 96 of an Olympus BHSM microscope, equipped with 10x and 50x objectives and part of a 97 Renishaw 1000 Raman microscope system, which also includes a monochromator, a filter 98 system and a Charge Coupled Device (CCD). Further details have been published. 99 100 101 Band component analysis was undertaken using the Jandel ‘Peakfit’ (Erkrath, 102 Germany) software package which enabled the type of fitting function to be selected and 103 allowed specific parameters to be fixed or varied accordingly. Band fitting was done using a 104 Lorentz-Gauss cross-product function with the minimum number of component bands used 105 for the fitting process. The Lorentz-Gauss ratio was maintained at values greater than 0.7 and 106 fitting was undertaken until reproducible results were obtained with squared correlations ( r2) 107 greater than 0.995. Band fitting of the spectra is quite reliable providing there is some band 108 separation or changes in the spectral profile. 109

110 3. Results and discussion 111 112 The complete Raman spectrum of lewisite over the full wavenumber range is shown 113 in Figure 1. This figure shows the relative intensities of the Raman bands. It is observed that

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114 the bands attributed to the antimonate anion are significantly more intense than the bands in 115 the OH stretching region. The Raman spectrum of lewisite in the 100 to 1100 cm-1 range is 116 reported in Figure 2. The Raman spectrum of bindheimite, stibiconite, roméite is displayed 117 in Figurers 3, 4 and 5 respectively. A series of bands for lewisite are observed with the most 118 intense band at 517 cm-1. Other Raman bands are observed at 565, 611, 725, 806 and 984 119 cm-1. According to Siebert (17, 18) all bands in these positions are assignable to SbO 120 stretching modes. The observation of multiple bands in the Raman spectrum of lewisite 121 provides evidence for the non-equivalence of SbO units in its structure. 122 123 In the infrared spectrum of antimony pentoxide an intense band is observed at 740 cm-1 and 124 low intensity bands at ~370, 450 and 680 cm-1 (19). The infrared spectrum of valentinite

125 (Sb2O3)4 showed bands in similar positions (19). Farmer reported the band positions of

126 synthetic antimonates of formula MSbO4 where M is Cr, Fe, Ga or Rh with a rutile type

127 structure (20). As such these structures should have four Raman active bands (A1g + B1g +

128 B2g + Eg) and four infrared active bands (A2u + 3Eu). Infrared bands were observed in the 660 129 to 735 cm-1, 520 to 585 cm-1, 285 to 375 cm-1 and 170 to 190 cm-1. Although no assignment 130 was given to these bands but one possible interpretation is that the first band is attributed to 131 the antisymmetric stretching mode, the second to the symmetric stretching mode, the third to 132 bending modes and the fourth to a lattice modes. 133 134 Hence the bands of lewisite at 517 cm-1 are attributable the symmetric stretching modes. A 135 band in a similar position is found in the Raman spectrum of bindheimite at 512 cm-1 (Figure 136 3). However, the most intense band for this mineral is found at 656 cm-1. The most intense 137 Raman band in the spectrum of stibiconite (Figure 4) is found at 199 cm-1. A band is 138 observed for stibiconite at 522 cm-1 which is also attributed to the SbO stretching vibrational 139 mode. The least complex Raman spectrum of the antimony bearing minerals is found for the 140 mineral roméite (Figure 5). A very intense band is observed at 518 cm-1 which is attributed 141 to the SbO stretching vibration. The additional bands at higher wavenumbers at 565, 611 and 142 725 cm-1 may also be assigned to SbO stretching vibrations. 143 144 In the Raman spectrum of lewisite bands of medium intensity are observed at 300, 356 and 145 400 cm-1. These bands are attributed to OSbO bending vibrations. In the Raman spectrum 146 of bindheimite a series of bands are found at 293, 312, 328 and 351 cm-1. These bands are

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147 not observed for stibiconite. However a band is found at 400 cm-1. A low intensity band is 148 found at 303 cm-1 for roméite. 149 150 The Raman spectrum of lewisite in the OH stretching region is displayed in Figure 6. Raman 151 bands are observed at 3200, 3328, 3471 cm-1 with a distinct shoulder at 3542 cm-1. This last 152 shoulder band is assigned to the stretching vibration of OH units. The first three bands are 153 attributed to water stretching vibrations. The observation of bands in the 3200 to 3500 cm-1 154 region suggests that water is involved in the lewisite structure. If this is the case then the 2+ 155 formula may be better written as Ca, Fe , Na)2(Sb, Ti)2(O,OH)7 ·xH2O. The observation of 156 water bands in the OH stretching region is supported by the observation of a water bending 157 mode at 1599 cm-1 (Figure 7). The position of this band is indicative of very weakly 158 hydrogen bonded water molecules. The two low intensity bands at 1353 and 1447 cm-1 are 159 assigned to overtone or combination bands. 160 161 4. Conclusions 162 2+ 163 The mineral lewisite (Ca, Fe , Na)2(Sb, Ti)2(O,OH)7 has been studied by Raman 164 spectroscopy and a comparison is made with the Raman spectra of other antimony containing 165 minerals. The mineral lewisite has classically been given the formula mineral (Ca, Fe2+,

166 Na)2(Sb, Ti)2O7. However Raman spectroscopy identifies bands assignable to water 167 stretching and bending vibrations. This suggests that water is involved in the structure of 2+ 168 lewisite and the formula may be better written (Ca, Fe , Na)2(Sb, Ti)2(O,OH)7 ·xH2O. 169 170 Intense Raman band at 656 cm-1 is assigned to SbO stretching vibrations. Other lower 171 intensity bands at 664, 749 and 814 cm-1 may also be assigned to this vibration. This 172 observation suggests the non-equivalence of SbO units in the structure. Low intensity 173 Raman bands at 293, 312 and 328 cm-1 are probably assignable to the OSbO bending 174 vibrations. Infrared bands at 984, 1353, 1447 and 1599 cm-1 are attributed to δ OH 175 deformation modes. 176 177 Acknowledgements 178 179 The financial and infra-structure support of the Queensland University of Technology 180 Inorganic Materials Research Program of the School of Physical and Chemical Sciences is 6

181 gratefully acknowledged. The Australian Research Council (ARC) is thanked for funding the 182 instrumentation. Mr. Ben McHenry of The South Australian Museum is thanked for the loan 183 of the antimony containing mineral, lewisite. 184 185

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186 References 187 188 (1) Rouse, R. C., Dunn, P. J., Peacor, D. R., Wang, L., J. Solid State Chem. 1998, 141,

189 562-569.

190 (2) Zubkova, N. V., Pushcharovsky, D. Y., Atencio, D., Arakcheeva, A. V., Matioli, P.

191 A., J. Alloys Comp. 2000, 296, 75-79.

192 (3) Cody, C. A., DiCarlo, L., Darlington, R. K., Inorg. Chem. 1979, 18, 1572-1576.

193 (4) Correia, A. M., Oliveira, M. J. V., Clark, R. J. H., Ribeiro, M. I., Duarte, M. L., Anal.

194 Chem. 2008, 80, 1482-1492.

195 (5) Correia, A. M., Clark, R. J. H., Ribeiro, M. I. M., Duarte, M. L. T. S., J. Raman

196 Spectrosc.2007, 38, 1390-1405.

197 (6) Clark, R. J. H., Cridland, L., Kariuki, B. M., Harris, K. D. M., Withnall, R., J.

198 Chem.Soc. 1995, 2577-2582.

199 (7) Husson, E., Repelin, Y., Vandenborre, M. T., Spectrochim. Acta, 1984, 40A, 1017-

200 1020.

201 (8) Haeuseler, H., Spectrochim. Acta, 1981, 37A, 487-495.

202 (9) Vandenborre, M. T., Husson, E., Brusset, H., Cerez, A., Spectrochim. Acta, 1980,

203 36A, 1045-1052.

204 (10) Paques-Ledent, M. T., Tarte, P., Spectrochim. Acta, Part A 1974, 30A, 673-689.

205 (11) Gevork'yan, S. V., Povarennykh, A. S., Konst. Svoistva Miner. 1975, 9, 73-81.

206 (12) Braithwaite, R. S. W., Mineral. Mag. 1983, 47, 51-57.

207 (13) Sumin De Portilla, V. I., Can. Mineral. 1974, 12, 262-268.

208 (14) Anthony, J. W., Bideaux, R. A., Bladh, K. W., Nichols, M. C., Handbook of

209 mineralogy, 2000.

210 (15) Anthony, J. W., Bideaux, R. A., Bladh, K. W., Nichols, M. C., Handbook of

211 mineralogy, Mineral Data publishing, Tuscon, Arizona, 1997.

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212 (16) Vitaliano, C. J., Mason, B., Am. Mineral. 1952, 37, 982-999.

213 (17) Siebert, H., Z. anorg. u. allgem. Chem. 1959, 301, 161-170.

214 (18) Siebert, H., Anwendungen der Schwingungsspektroskopie in der Anorganischen

215 Chemie (Anorganische und Allgemeine Chemie in Einzeldarstellungen, Bd. 7)

216 (Application of Vibrational Spectroscopy in Inorganic Chemistry (Monographs in

217 Inorganic and General Chemistry, Vol. 7)), 1966.

218 (19) Gadsden, J. A., Infrared spectra of minerals and related inorganic compounds,

219 Buttherworth, London, UK, 1975.

220 (20) Farmer, V. C., Mineralogical Society Monograph 4: The Infrared Spectra of Minerals,

221 London, 1974.

222

223 224 225

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226 Table 1 Antimonates with the formula (A)2 (X2O6) (O,OH,F) 227 Mineral Name Chemical Composition Crystal Space Z System Group 3+ 5+ Stibiconite Sb Sb 2O6(OH) Isometric F d3m 8

Bindheimite Pb2Sb2O6(O,OH) Isometric F d3m 6

2+ Romeite (Ca, Fe , Mn, Na)2(Sb, Isometric F d3m 11

Ti)2O6(O, OH, F) 2+ Lewisite (Ca, Fe , Na)2(Sb, Ti)2O7 Isometric F d3m 8

Monimolite (Pb, Ca)2Sb2O7 Isometric F d3m 8

Stetefeldite Ag2Sb2O6(O,OH) Isometric F d3m 6

5+ 3+ Bismutostibiconite Bi(Sb , Fe )2O7 Isometric F d3m 8

Partzite Cu2Sb2(O, OH)7 Isometric F d3m 8

2+ 5+ Ingersonite Ca3Mn Sb 4O14 Trigonal P 3m 3

228 229

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230 List of Figures 231 232 Figure 1 Raman spectrum of lewisite over the full wavelength range, showing the relative 233 intensity of the bands. 234 235 Figure 2 Band fitted Raman spectrum of lewisite in the 100 to 1700 cm-1 region. 236 237 Figure 3 Band fitted Raman spectrum of bindheimite in the 100 to 900 cm-1 region. 238 239 Figure 4 Band fitted Raman spectrum of bindheimite in the 50 to 900 cm-1 region. 240 241 Figure 5 Band fitted Raman spectrum of romeite in the 50 to 900 cm-1 region. 242 243 Figure 6 Band fitted Raman spectrum of lewisite in the 3000 to 3800 cm-1 region. 244 245 Figure 7 Band fitted Raman spectrum of lewisite in the 900 to 1700 cm-1 region. 246 247 248 249 250 251

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252 253 254 Figure 1 255 256

12

257 258 259 Figure 2 260 261

13

262 263 264 Figure 3 265 266

14

267 268 269 Figure 4 270 271

15

272 273 274 Figure 5 275 276

16

277

278 279 280 Figure 6 281 282

17

283 284 285 Figure 7 286

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