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A Raman spectroscopic study of the mineral coquandite Sb6O8(SO4)·(H2O)
Spectrochimica Acta Part A 75 (2010) 852–854
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
A Raman spectroscopic study of the mineral coquandite Sb6 O8 (SO4 )·(H2 O) Ray L. Frost ∗ , Silmarilly Bahfenne Inorganic Materials Research Program, School of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434, 2 George St., Brisbane, Queensland 4001, Australia
a r t i c l e
i n f o
Article history: Received 3 September 2009 Received in revised form 20 November 2009 Accepted 1 December 2009 Keywords: Coquandite Raman spectroscopy Antimonite Archaeology
a b s t r a c t Raman spectra of coquandite Sb6 O8 (SO4 )·(H2 O) were studied, and related to the structure of the mineral. Raman bands observed at 970, 990 and 1007 cm−1 and a series of overlapping bands are observed at 1072, 1100, 1151 and 1217 cm−1 are assigned to the SO4 2− 1 symmetric and 3 antisymmetric stretching modes respectively. Raman bands at 629, 638, 690, 751 and 787 cm−1 are attributed to the SbO stretching vibrations. Raman bands at 600 and 610 cm−1 and at 429 and 459 cm−1 are assigned to the SO4 2− 4 and 2 bending modes. Raman bands at 359 and 375 cm−1 are assigned to O–Sb–O bending modes. Multiple Raman bands for both SO4 2− and SbO stretching vibrations support the concept of the non-equivalence of these units in the coquandite structure. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Coquandite is an oxy-sulphate hydrate, occurs as spheroidal knobs of silky fibers or, rarely, as tiny transparent colourless lamellar crystals on stibnite. The mineral coquandite Sb6 3+ O8 (SO4 )·H2 O [1] is triclinic [2] with a 11.434(7), b 29.77(4), c 11.314(4) Å, ˛ 91.07(7)◦ , ˇ 119.24(3)◦ , and 92.82(1)◦ . It has a cell volume of 3352(5)Å3 with Z = 12. The crystals are lamellar and elongated along the 0 0 1 axis. According to Sabelli et al. the structure of the mineral consists of polyhedra arranged in nine layers perpendicular to [0 1 0] and form ‘hexagonally’ shaped groups surrounded by SO4 2− tetrahedra. The mineral displays a fibrous morphology in feathery spheroidal aggregates [2]. The mineral has a silky appearance and is often found with stibnite Sb2 S3 . The mineral has been identified at several localities including the Lucky Knock Mine, Tonasket, Okanogan Co., Washington, USA and Petera Mine, Italy [3]. The mineral is from an ancient mine site at Pereta, Tuscany, Italy, [1] where minerals including S and cinnabar were mined in ancient times. Activities continued during the middle ages and Renaissance through 1942 and then concluded in 1960–1970 with open trenches. Rare minerals such as fluellite Al2 (PO4 )F2 (OH)·7H2 O, gearksutite CaAl(OH)F4 ·H2 O, minyulite KAl2 (PO4 )2 (OH,F)·4H2 O, mopungite NaSb(OH)6 , tripuhyite FeSb2 O6 have been found at this mine site together with two new mineral species, peretaite Ca(SbO)4 (OH)2 (SO4 )2 ·2H2 O and coquandite [1].
∗ Corresponding author. Tel.: +61 7 3138 2407; fax: +61 7 3138 1804. E-mail address: [email protected] (R.L. Frost). 1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2009.12.012
It is interesting to note that very few papers have been published on the spectroscopy of antimonite minerals. What research has been published is related to the analysis of pigments [4–6]. Very few studies of related minerals such as mineral arsenites have not been undertaken using vibrational spectroscopy [7–9], even though Raman spectroscopy has proven especially useful for the study of minerals [10–18]. The aim of this paper is to report the Raman spectra of coquandite and to relate the spectra to the chemistry and molecular structure of the mineral. This paper follows the systematic research on Raman and infrared spectroscopy of secondary minerals containing oxy-anions formed in the oxidation zone of minerals. 2. Experimental 2.1. Minerals The mineral coquandite was obtained from the Mineralogical Research Company. The mineral originated from the Pereta Mine, Italy. The composition of the mineral has been published [2, p. 137]. 2.2. Raman spectroscopy Crystals of coquandite were placed on a polished metal surface on the stage of an Olympus BHSM microscope, which is equipped with 10×, 20×, and 50× objectives. The microscope is part of a Renishaw 1000 Raman microscope system, which also includes a monochromator, a filter system and a CCD detector (1024 pixels). The Raman spectra were excited by a Spectra-Physics model 127 He–Ne laser producing highly polarised light at 633 nm and col-
R.L. Frost, S. Bahfenne / Spectrochimica Acta Part A 75 (2010) 852–854
853
Fig. 1. Raman spectra of coquandite over the 100–4000 cm−1 range.
Fig. 2. Raman spectra of coquandite over the 800–1700 cm−1 range.
lected at a nominal resolution of 2 cm−1 and a precision of ±1 cm−1 in the range between 100 and 4000 cm−1 . Repeated acquisition on the crystals using the highest magnification (50×) were accumulated to improve the signal to noise ratio in the spectra. Spectra were calibrated using the 520.5 cm−1 line of a silicon wafer. Further details have been published [10–18]. Alignment of all crystals in a similar orientation has been attempted and achieved. This was achieved by placing a small crystal on the end of a fine needle and rotating the needle to obtain the required orientation. Differences in intensity may be observed due to minor differences in the crystal orientation. Band component analysis was undertaken using the Jandel ‘Peakfit’ (Erkrath, Germany) software package which enabled the type of fitting function to be selected and allowed specific parameters to be fixed or varied accordingly. Band fitting was done using a Lorentz–Gauss cross-product function with the minimum number of component bands used for the fitting process. The Lorentz–Gauss ratio was maintained at values greater than 0.7 and fitting was undertaken until reproducible results were obtained with squared correlations (r2 ) greater than 0.995. Band fitting of the spectra is quite reliable providing there is some band separation or changes in the spectral profile.
ing to Siebert [19,20] all bands in these positions are assignable to stretching vibrations. The observation of multiple bands in the Raman spectrum provides evidence for the non-equivalence of SbO units in the coquandite structure. In the infrared spectrum of antimony pentoxide an intense band is observed at 740 cm−1 and low intensity bands at ∼370, 450 and 680 cm−1 [21]. The infrared spectrum of valentinite (Sb2 O3 )4 showed bands in similar positions [21]. Farmer reported the band positions of synthetic antimonates of formula MSbO4 where M is Cr, Fe, Ga or Rh with a rutile type structure [22]. As such these structures should have four Raman active bands (A1g + B1g + B2g + Eg ) and four infrared active bands (A2u + 3Eu ). Infrared bands were observed in the 660–735, 520–585, 285–375 and 170–190 cm−1 . Although no assignment was given to these bands but one possible interpretation is that the first band is attributed to the antisymmetric stretching mode, the second to the symmetric stretching mode, the third to bending modes and the fourth to a lattice modes. Hence the bands of coquandite at around 618 cm−1 are attributable the symmetric stretching modes. The observation of several bands in this region suggests that the SbO are not equivalent. The difficulty with the assignment of the bands at 600 and 610 cm−1 is that these bands may also be ascribed to sulphate bending vibrations. The Raman spectroscopy of the aqueous sulphate tetrahedral oxy-anion yields the symmetric stretching (1 ) vibration at 981 cm−1 , the symmetric bending (2 ) mode at 451 cm−1 , the antisymmetric stretching (3 ) mode at 1104 cm−1 and the antisymmetric bending (4 ) mode at 613 cm−1 . The two bands at 429 and 459 cm−1 are assigned to the 2 bending mode. The Raman bands at 359 and 375 cm−1 may be attributed to O–Sb–O bending
3. Results and discussion The complete Raman spectrum is shown in Fig. 1. This figure shows the relative intensity of the different bands in the spectrum and shows why the spectrum is divided into sections as parts of the spectrum contain no bands. The Raman spectrum in the 800–1700 cm−1 region is displayed in Fig. 2. The mineral coquandite should be thought of as a sulphate of antimony III oxide. The Raman spectrum in the 980 to 1020 cm−1 region is complex with a series of overlapping bands. Deconvoluted bands are observed at 970, 990 and 1007 cm−1 . These bands are attributed to the SO4 2− 1 symmetric stretching mode. The observation of multiple sulphate bands provides evidence for the non-equivalence of sulphate anions in the molecular structure of coquandite. A series of overlapping bands are observed at 1072, 1100, 1151 and 1217 cm−1 . Other component bands are observed at 1168 cm−1 but are of low intensity. These bands are attributed to the SO4 2− 3 antisymmetric stretching mode. The observation of multiple bands in this spectral region supports the concept of different sulphate units in the molecular structure of coquandite. The low wavenumber Raman spectral region is displayed in Fig. 3. A series of Raman bands in the 600–800 cm−1 range are observed. Bands at 600, 610, 629, 638, 690, 751 and 787 cm−1 are found. These bands are assigned to SbO vibrations. Accord-
Fig. 3. Raman spectra of coquandite over the 100–800 cm−1 range.
854
R.L. Frost, S. Bahfenne / Spectrochimica Acta Part A 75 (2010) 852–854
structure of the mineral. Raman bands were attributed to the sulphate stretching and bending modes. As well Raman bands were assigned to SbO stretching and bending vibrations. Multiple Raman bands for both SO4 2− and SbO stretching vibrations support the concept of the non-equivalence of these units in the coquandite structure. Acknowledgements The financial and infra-structure support of the Queensland University of Technology Inorganic Materials Research Program of the School of Physical and Chemical Sciences is gratefully acknowledged. The Australian Research Council (ARC) is thanked for funding the instrumentation. References Fig. 4. Raman spectra of coquandite over the 2700–3600 cm−1 range.
modes. Intense Raman bands are observed for the mineral brandholzite Mg[Sb(OH)6 ]·6H2 O at 303, 318 and 340 cm−1 . These bands were assigned to OSbO bending modes. Such an assessment fits well with the assignment of bands for MSbO4 structures as reported by Farmer [22]. The observation of multiple bands suggests the nonequivalence of SbO units in the brandholzite structure. The very low wavenumber region in the 100 to around 300 cm−1 is complex. Prominent bands are observed at 129, 149, 167, 178, 203, 216 and 253 cm−1 . These bands are described as lattice modes. The Raman spectrum of the OH stretching region is shown in Fig. 4. The spectrum is very noisy but nevertheless Raman bands are observed at 2764, 2900, 2961, 3122, 3193, 3318 and 3449 cm−1 . These bands may be attributed to the water OH stretching vibrations. The observation of multiple bands supports the concept of the non-equivalence of the water molecules in the coquandite structure. Such observations cannot be made with X-ray diffraction. 4. Conclusions The mineral coquandite Sb6 O8 (SO4 )·(H2 O) is formed through the action of sulphuric acid on stibnite Sb2 S3 . The mineral is colourless to white and may be easily confused with like minerals. Raman spectroscopy enables the mineral coquandite to be identified. Raman spectra have been studied and related to the molecular
[1] G. Brizzi, R. Meli, Rivista Min. Ita. (1995) 217–238. [2] J.W. Anthony, R.A. Bideaux, K.W. Bladh, M.C. Nichols, Handbook of Mineralogy, Mineral Data Publishing, Tuscon, Arizona, USA, 2000. [3] C. Sabelli, P. Orlandi, G. Vezzalini, Min. Mag. 56 (1992) 599–693. [4] A.M. Correia, M.J.V. Oliveira, R.J.H. Clark, M.I. Ribeiro, M.L. Duarte, Anal. Chem. 80 (2008) 1482–1492. [5] A.M. Correia, R.J.H. Clark, M.I.M. Ribeiro, M.L.T.S. Duarte, J. Raman Spectrosc. 38 (2007) 1390–1405. [6] R.J.H. Clark, L. Cridland, B.M. Kariuki, K.D.M. Harris, R. Withnall, J. Chem. Soc. (1995) 2577–2582. [7] M.T. Paques-Ledent, P. Tarte, Spectrochim. Acta 30A (1974) 673–689. [8] S.V. Gevork’yan, A.S. Povarennykh, Konst. Svoistva Miner. 9 (1975) 73–81. [9] R.S.W. Braithwaite, Min. Mag. 47 (1983) 51–57. [10] R.L. Frost, J. Cejka, G. Ayoko, J. Raman Spectrosc. 39 (2008) 495–502. [11] R.L. Frost, J. Cejka, G.A. Ayoko, M.J. Dickfos, J. Raman Spectrosc. 39 (2008) 374–379. [12] R.L. Frost, J. Cejka, M.J. Dickfos, J. Raman Spectrosc. 39 (2008) 779–785. [13] R.L. Frost, M.J. Dickfos, J. Cejka, J. Raman Spectrosc. 39 (2008) 582–586. [14] R.L. Frost, M.C. Hales, D.L. Wain, J. Raman Spectrosc. 39 (2008) 108–114. [15] S. Bahfenne, R.L. Frost, Spectrochim. Acta, Part A 74 (2009) 100–103. [16] R.L. Frost, A. Locke, W.N. Martens, J. Raman Spectrosc. 39 (2008) 901–908. [17] R.L. Frost, B.J. Reddy, M.J. Dickfos, J. Raman Spectrosc. 39 (2008) 909–913. [18] S.J. Palmer, R.L. Frost, G. Ayoko, T. Nguyen, J. Raman Spectrosc. 39 (2008) 395–401. [19] H. Siebert, Z. anorg. u. allgem. Chem. 301 (1959) 161–170. [20] H. Siebert, Anwendungen der Schwingungsspektroskopie in der Anorganischen Chemie (Anorganische und Allgemeine Chemie in Einzeldarstellungen, Bd. 7), Application of Vibrational Spectroscopy in Inorganic Chemistry, Monographs in Inorganic and General Chemistry, vol. 7, 1966. [21] J.A. Gadsden, Infrared Spectra of Minerals and Related Inorganic Compounds, Buttherworth, London, UK, 1975. [22] V.C. Farmer, Mineralogical Society Monograph 4: The Infrared Spectra of Minerals, 1974.
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
A Raman spectroscopic study of the mineral coquandite Sb6 O8 (SO4 )·(H2 O) Ray L. Frost ∗ , Silmarilly Bahfenne Inorganic Materials Research Program, School of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434, 2 George St., Brisbane, Queensland 4001, Australia
a r t i c l e
i n f o
Article history: Received 3 September 2009 Received in revised form 20 November 2009 Accepted 1 December 2009 Keywords: Coquandite Raman spectroscopy Antimonite Archaeology
a b s t r a c t Raman spectra of coquandite Sb6 O8 (SO4 )·(H2 O) were studied, and related to the structure of the mineral. Raman bands observed at 970, 990 and 1007 cm−1 and a series of overlapping bands are observed at 1072, 1100, 1151 and 1217 cm−1 are assigned to the SO4 2− 1 symmetric and 3 antisymmetric stretching modes respectively. Raman bands at 629, 638, 690, 751 and 787 cm−1 are attributed to the SbO stretching vibrations. Raman bands at 600 and 610 cm−1 and at 429 and 459 cm−1 are assigned to the SO4 2− 4 and 2 bending modes. Raman bands at 359 and 375 cm−1 are assigned to O–Sb–O bending modes. Multiple Raman bands for both SO4 2− and SbO stretching vibrations support the concept of the non-equivalence of these units in the coquandite structure. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Coquandite is an oxy-sulphate hydrate, occurs as spheroidal knobs of silky fibers or, rarely, as tiny transparent colourless lamellar crystals on stibnite. The mineral coquandite Sb6 3+ O8 (SO4 )·H2 O [1] is triclinic [2] with a 11.434(7), b 29.77(4), c 11.314(4) Å, ˛ 91.07(7)◦ , ˇ 119.24(3)◦ , and 92.82(1)◦ . It has a cell volume of 3352(5)Å3 with Z = 12. The crystals are lamellar and elongated along the 0 0 1 axis. According to Sabelli et al. the structure of the mineral consists of polyhedra arranged in nine layers perpendicular to [0 1 0] and form ‘hexagonally’ shaped groups surrounded by SO4 2− tetrahedra. The mineral displays a fibrous morphology in feathery spheroidal aggregates [2]. The mineral has a silky appearance and is often found with stibnite Sb2 S3 . The mineral has been identified at several localities including the Lucky Knock Mine, Tonasket, Okanogan Co., Washington, USA and Petera Mine, Italy [3]. The mineral is from an ancient mine site at Pereta, Tuscany, Italy, [1] where minerals including S and cinnabar were mined in ancient times. Activities continued during the middle ages and Renaissance through 1942 and then concluded in 1960–1970 with open trenches. Rare minerals such as fluellite Al2 (PO4 )F2 (OH)·7H2 O, gearksutite CaAl(OH)F4 ·H2 O, minyulite KAl2 (PO4 )2 (OH,F)·4H2 O, mopungite NaSb(OH)6 , tripuhyite FeSb2 O6 have been found at this mine site together with two new mineral species, peretaite Ca(SbO)4 (OH)2 (SO4 )2 ·2H2 O and coquandite [1].
∗ Corresponding author. Tel.: +61 7 3138 2407; fax: +61 7 3138 1804. E-mail address: [email protected] (R.L. Frost). 1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2009.12.012
It is interesting to note that very few papers have been published on the spectroscopy of antimonite minerals. What research has been published is related to the analysis of pigments [4–6]. Very few studies of related minerals such as mineral arsenites have not been undertaken using vibrational spectroscopy [7–9], even though Raman spectroscopy has proven especially useful for the study of minerals [10–18]. The aim of this paper is to report the Raman spectra of coquandite and to relate the spectra to the chemistry and molecular structure of the mineral. This paper follows the systematic research on Raman and infrared spectroscopy of secondary minerals containing oxy-anions formed in the oxidation zone of minerals. 2. Experimental 2.1. Minerals The mineral coquandite was obtained from the Mineralogical Research Company. The mineral originated from the Pereta Mine, Italy. The composition of the mineral has been published [2, p. 137]. 2.2. Raman spectroscopy Crystals of coquandite were placed on a polished metal surface on the stage of an Olympus BHSM microscope, which is equipped with 10×, 20×, and 50× objectives. The microscope is part of a Renishaw 1000 Raman microscope system, which also includes a monochromator, a filter system and a CCD detector (1024 pixels). The Raman spectra were excited by a Spectra-Physics model 127 He–Ne laser producing highly polarised light at 633 nm and col-
R.L. Frost, S. Bahfenne / Spectrochimica Acta Part A 75 (2010) 852–854
853
Fig. 1. Raman spectra of coquandite over the 100–4000 cm−1 range.
Fig. 2. Raman spectra of coquandite over the 800–1700 cm−1 range.
lected at a nominal resolution of 2 cm−1 and a precision of ±1 cm−1 in the range between 100 and 4000 cm−1 . Repeated acquisition on the crystals using the highest magnification (50×) were accumulated to improve the signal to noise ratio in the spectra. Spectra were calibrated using the 520.5 cm−1 line of a silicon wafer. Further details have been published [10–18]. Alignment of all crystals in a similar orientation has been attempted and achieved. This was achieved by placing a small crystal on the end of a fine needle and rotating the needle to obtain the required orientation. Differences in intensity may be observed due to minor differences in the crystal orientation. Band component analysis was undertaken using the Jandel ‘Peakfit’ (Erkrath, Germany) software package which enabled the type of fitting function to be selected and allowed specific parameters to be fixed or varied accordingly. Band fitting was done using a Lorentz–Gauss cross-product function with the minimum number of component bands used for the fitting process. The Lorentz–Gauss ratio was maintained at values greater than 0.7 and fitting was undertaken until reproducible results were obtained with squared correlations (r2 ) greater than 0.995. Band fitting of the spectra is quite reliable providing there is some band separation or changes in the spectral profile.
ing to Siebert [19,20] all bands in these positions are assignable to stretching vibrations. The observation of multiple bands in the Raman spectrum provides evidence for the non-equivalence of SbO units in the coquandite structure. In the infrared spectrum of antimony pentoxide an intense band is observed at 740 cm−1 and low intensity bands at ∼370, 450 and 680 cm−1 [21]. The infrared spectrum of valentinite (Sb2 O3 )4 showed bands in similar positions [21]. Farmer reported the band positions of synthetic antimonates of formula MSbO4 where M is Cr, Fe, Ga or Rh with a rutile type structure [22]. As such these structures should have four Raman active bands (A1g + B1g + B2g + Eg ) and four infrared active bands (A2u + 3Eu ). Infrared bands were observed in the 660–735, 520–585, 285–375 and 170–190 cm−1 . Although no assignment was given to these bands but one possible interpretation is that the first band is attributed to the antisymmetric stretching mode, the second to the symmetric stretching mode, the third to bending modes and the fourth to a lattice modes. Hence the bands of coquandite at around 618 cm−1 are attributable the symmetric stretching modes. The observation of several bands in this region suggests that the SbO are not equivalent. The difficulty with the assignment of the bands at 600 and 610 cm−1 is that these bands may also be ascribed to sulphate bending vibrations. The Raman spectroscopy of the aqueous sulphate tetrahedral oxy-anion yields the symmetric stretching (1 ) vibration at 981 cm−1 , the symmetric bending (2 ) mode at 451 cm−1 , the antisymmetric stretching (3 ) mode at 1104 cm−1 and the antisymmetric bending (4 ) mode at 613 cm−1 . The two bands at 429 and 459 cm−1 are assigned to the 2 bending mode. The Raman bands at 359 and 375 cm−1 may be attributed to O–Sb–O bending
3. Results and discussion The complete Raman spectrum is shown in Fig. 1. This figure shows the relative intensity of the different bands in the spectrum and shows why the spectrum is divided into sections as parts of the spectrum contain no bands. The Raman spectrum in the 800–1700 cm−1 region is displayed in Fig. 2. The mineral coquandite should be thought of as a sulphate of antimony III oxide. The Raman spectrum in the 980 to 1020 cm−1 region is complex with a series of overlapping bands. Deconvoluted bands are observed at 970, 990 and 1007 cm−1 . These bands are attributed to the SO4 2− 1 symmetric stretching mode. The observation of multiple sulphate bands provides evidence for the non-equivalence of sulphate anions in the molecular structure of coquandite. A series of overlapping bands are observed at 1072, 1100, 1151 and 1217 cm−1 . Other component bands are observed at 1168 cm−1 but are of low intensity. These bands are attributed to the SO4 2− 3 antisymmetric stretching mode. The observation of multiple bands in this spectral region supports the concept of different sulphate units in the molecular structure of coquandite. The low wavenumber Raman spectral region is displayed in Fig. 3. A series of Raman bands in the 600–800 cm−1 range are observed. Bands at 600, 610, 629, 638, 690, 751 and 787 cm−1 are found. These bands are assigned to SbO vibrations. Accord-
Fig. 3. Raman spectra of coquandite over the 100–800 cm−1 range.
854
R.L. Frost, S. Bahfenne / Spectrochimica Acta Part A 75 (2010) 852–854
structure of the mineral. Raman bands were attributed to the sulphate stretching and bending modes. As well Raman bands were assigned to SbO stretching and bending vibrations. Multiple Raman bands for both SO4 2− and SbO stretching vibrations support the concept of the non-equivalence of these units in the coquandite structure. Acknowledgements The financial and infra-structure support of the Queensland University of Technology Inorganic Materials Research Program of the School of Physical and Chemical Sciences is gratefully acknowledged. The Australian Research Council (ARC) is thanked for funding the instrumentation. References Fig. 4. Raman spectra of coquandite over the 2700–3600 cm−1 range.
modes. Intense Raman bands are observed for the mineral brandholzite Mg[Sb(OH)6 ]·6H2 O at 303, 318 and 340 cm−1 . These bands were assigned to OSbO bending modes. Such an assessment fits well with the assignment of bands for MSbO4 structures as reported by Farmer [22]. The observation of multiple bands suggests the nonequivalence of SbO units in the brandholzite structure. The very low wavenumber region in the 100 to around 300 cm−1 is complex. Prominent bands are observed at 129, 149, 167, 178, 203, 216 and 253 cm−1 . These bands are described as lattice modes. The Raman spectrum of the OH stretching region is shown in Fig. 4. The spectrum is very noisy but nevertheless Raman bands are observed at 2764, 2900, 2961, 3122, 3193, 3318 and 3449 cm−1 . These bands may be attributed to the water OH stretching vibrations. The observation of multiple bands supports the concept of the non-equivalence of the water molecules in the coquandite structure. Such observations cannot be made with X-ray diffraction. 4. Conclusions The mineral coquandite Sb6 O8 (SO4 )·(H2 O) is formed through the action of sulphuric acid on stibnite Sb2 S3 . The mineral is colourless to white and may be easily confused with like minerals. Raman spectroscopy enables the mineral coquandite to be identified. Raman spectra have been studied and related to the molecular
[1] G. Brizzi, R. Meli, Rivista Min. Ita. (1995) 217–238. [2] J.W. Anthony, R.A. Bideaux, K.W. Bladh, M.C. Nichols, Handbook of Mineralogy, Mineral Data Publishing, Tuscon, Arizona, USA, 2000. [3] C. Sabelli, P. Orlandi, G. Vezzalini, Min. Mag. 56 (1992) 599–693. [4] A.M. Correia, M.J.V. Oliveira, R.J.H. Clark, M.I. Ribeiro, M.L. Duarte, Anal. Chem. 80 (2008) 1482–1492. [5] A.M. Correia, R.J.H. Clark, M.I.M. Ribeiro, M.L.T.S. Duarte, J. Raman Spectrosc. 38 (2007) 1390–1405. [6] R.J.H. Clark, L. Cridland, B.M. Kariuki, K.D.M. Harris, R. Withnall, J. Chem. Soc. (1995) 2577–2582. [7] M.T. Paques-Ledent, P. Tarte, Spectrochim. Acta 30A (1974) 673–689. [8] S.V. Gevork’yan, A.S. Povarennykh, Konst. Svoistva Miner. 9 (1975) 73–81. [9] R.S.W. Braithwaite, Min. Mag. 47 (1983) 51–57. [10] R.L. Frost, J. Cejka, G. Ayoko, J. Raman Spectrosc. 39 (2008) 495–502. [11] R.L. Frost, J. Cejka, G.A. Ayoko, M.J. Dickfos, J. Raman Spectrosc. 39 (2008) 374–379. [12] R.L. Frost, J. Cejka, M.J. Dickfos, J. Raman Spectrosc. 39 (2008) 779–785. [13] R.L. Frost, M.J. Dickfos, J. Cejka, J. Raman Spectrosc. 39 (2008) 582–586. [14] R.L. Frost, M.C. Hales, D.L. Wain, J. Raman Spectrosc. 39 (2008) 108–114. [15] S. Bahfenne, R.L. Frost, Spectrochim. Acta, Part A 74 (2009) 100–103. [16] R.L. Frost, A. Locke, W.N. Martens, J. Raman Spectrosc. 39 (2008) 901–908. [17] R.L. Frost, B.J. Reddy, M.J. Dickfos, J. Raman Spectrosc. 39 (2008) 909–913. [18] S.J. Palmer, R.L. Frost, G. Ayoko, T. Nguyen, J. Raman Spectrosc. 39 (2008) 395–401. [19] H. Siebert, Z. anorg. u. allgem. Chem. 301 (1959) 161–170. [20] H. Siebert, Anwendungen der Schwingungsspektroskopie in der Anorganischen Chemie (Anorganische und Allgemeine Chemie in Einzeldarstellungen, Bd. 7), Application of Vibrational Spectroscopy in Inorganic Chemistry, Monographs in Inorganic and General Chemistry, vol. 7, 1966. [21] J.A. Gadsden, Infrared Spectra of Minerals and Related Inorganic Compounds, Buttherworth, London, UK, 1975. [22] V.C. Farmer, Mineralogical Society Monograph 4: The Infrared Spectra of Minerals, 1974.