Raman spectroscopic study of the hydrogen‐arsenate mineral pharmacolite Ca(AsO3OH)·2H2O—implications for aquifer and sediment remediation

The removal of arsenate anions from aqueous media, sediments and wasted soils is of environmental significance. The reaction of gypsum with the arsenate anion results in pharmacolite mineral formation, together with related minerals. Raman and infrared (IR) spectroscopy have been used to study the mineral pharmacolite Ca(AsO₃OH)· 2H₂O. The mineral is characterised by an intense Raman band at 865 cm⁻¹ assigned to the ν₁ (AsO₃)²⁻ symmetric stretching mode. The equivalent IR band is found at 864 cm⁻¹. The low‐intensity Raman bands in the range from 844 to 886 cm⁻¹ provide evidence for ν₃ (AsO₃) antisymmetric stretching vibrations. A series of overlapping bands in the 300‐450 cm⁻¹ region are attributed to ν₂ and ν₄ (AsO₃) bending modes. Prominent Raman bands at around 3187 cm⁻¹ are assigned to the OH stretching vibrations of hydrogen‐bonded water molecules and the two sharp bands at 3425 and 3526 cm⁻¹ to the OH stretching vibrations of only weakly hydrogen‐bonded hydroxyls in (AsO₃OH)²⁻ units. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the antimonate mineral brandholzite Mg[Sb2(OH)12]·6H2O

Raman spectra of brandholzite Mg[Sb₂(OH)₁₂]·6H₂O were studied, complemented with infrared spectra, and related to the structure of the mineral. An intense Raman sharp band at 618 cm⁻¹ is attributed to the SbO symmetric stretching mode. The low‐intensity band at 730 cm⁻¹ is ascribed to the SbO antisymmetric stretching vibration. Low‐intensity Raman bands were found at 503, 526 and 578 cm⁻¹. Corresponding infrared bands were observed at 527, 600, 637, 693, 741 and 788 cm⁻¹. Four Raman bands observed at 1043, 1092, 1160 and 1189 cm⁻¹ and eight infrared bands at 963, 1027, 1055, 1075, 1108, 1128, 1156 and 1196 cm⁻¹ are assigned to δ SbOH deformation modes. A complex pattern resulting from the overlapping band of the water and hydroxyl units is observed. Raman bands are observed at 3240, 3383, 3466, 3483 and 3552 cm⁻¹; infrared bands at 3248, 3434 and 3565 cm⁻¹. The Raman bands at 3240 and 3383 cm⁻¹ and the infrared band at 3248 cm⁻¹ are assigned to water‐stretching vibrations. The two higher wavenumber Raman bands observed at 3466 and 3552 cm⁻¹ and two infrared bands at 3434 and 3565 cm⁻¹ are assigned to the stretching vibrations of the hydroxyl units. Observed Raman and infrared bands in the OH stretching region are associated with O‐H···O hydrogen bonds and their lengths 2.72, 2.79, 2.86, 2.88 and 3.0 Å (Raman) and 2.73, 2.83 and 3.07 Å (infrared). Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the magnesium carbonate mineral hydromagnesite (Mg5[(CO3)4(OH)2]· 4H2O)

Magnesium minerals are important for understanding the concept of geosequestration. One method of studying the hydrated hydroxy magnesium carbonate minerals is through vibrational spectroscopy. A combination of Raman and infrared spectroscopy has been used to study the mineral hydromagnesite. An intense band is observed at 1121 cm⁻¹, attributed to the CO₃²⁻ν₁ symmetric stretching mode. A series of infrared bands at 1387, 1413 and 1474 cm⁻¹ are assigned to the CO₃²⁻ν₃ antisymmetric stretching modes. The CO₃²⁻ν₃ antisymmetric stretching vibrations are extremely weak in the Raman spectrum and are observed at 1404, 1451, 1490 and 1520 cm⁻¹. A series of Raman bands at 708, 716, 728 and 758 cm⁻¹ are assigned to the CO₃²⁻ν₂ in‐plane bending mode. The Raman spectrum in the OH stretching region is characterized by bands at 3416, 3516 and 3447 cm⁻¹. In the infrared spectrum, a broad band is found at 2940 cm⁻¹, which is assigned to water stretching vibrations. Infrared bands at 3430, 3446, 3511, 2648 and 3685 cm⁻¹ are attributed to MgOH stretching modes. Copyright © 2011 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the antimonate mineral bahianite Al5Sb35+O14(OH)2

Raman spectroscopy has been used to characterize the antimonate mineral bahianite Al₅Sb₃⁵⁺O₁₄(OH)₂, a semi‐precious gemstone. The mineral is characterized by an intense Raman band at 818 cm⁻¹ assigned to Sb₃O₁₄¹³⁻ stretching vibrations. Other lower intensity bands at 843 and 856 cm⁻¹ are also assigned to this vibration, and this concept suggests the non‐equivalence of SbO units in the structure. Low‐intensity Raman bands at 669 and 682 cm⁻¹ are probably assignable to the OSbO antisymmetric stretching vibrations. Raman bands at 1756, 1808 and 1929 cm⁻¹ may be assigned to δ SbOH deformation modes, while the bands at 3462 and 3495 cm⁻¹ are assigned to AlOH stretching vibrations. The complexity in the low wave number region is attributed to the composition of the mineral. Copyright © 2009 John Wiley & Sons, Ltd.     

Dussertite BaFe3+3(AsO4)2(OH)5—a Raman spectroscopic study of a hydroxy‐arsenate mineral

The mineral dussertite, a hydroxy‐arsenate mineral with formula BaFe³⁺₃(AsO₄)₂(OH)₅, has been studied by Raman spectroscopy complemented with infrared spectroscopy. The spectra of three minerals from different origins were investigated and proved to be quite similar, although some minor differences were observed. In the Raman spectra of the Czech dussertite, four bands are observed in the 800–950 cm⁻¹ region. The bands are assigned as follows: the band at 902 cm⁻¹ is assigned to the (AsO₄)³⁻ν₃ antisymmetric stretching mode, the one at 870 cm⁻¹ to the (AsO₄)³⁻ν₁ symmetric stretching mode, and those at 859 and 825 cm⁻¹ to the As‐OM^{2 + /3+} stretching modes and/or hydroxyl bending modes. Raman bands at 372 and 409 cm⁻¹ are attributed to the ν₂ (AsO₄)³⁻ bending mode and the two bands at 429 and 474 cm⁻¹ are assigned to the ν₄ (AsO₄)³⁻ bending mode. An intense band at 3446 cm⁻¹ in the infrared spectrum and a complex set of bands centred upon 3453 cm⁻¹ in the Raman spectrum are attributed to the stretching vibrations of the hydrogen‐bonded (OH)⁻ units and/or water units in the mineral structure. The broad infrared band at 3223 cm⁻¹ is assigned to the vibrations of hydrogen‐bonded water molecules. Raman spectroscopy identified Raman bands attributable to (AsO₄)³⁻ and (AsO₃OH)²⁻ units. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman spectroscopic study of synthetic reevesite and cobalt substituted reevesite (Ni,Co)6Fe2(OH)16(CO3)·4H2O

Raman spectroscopy, complemented with infrared spectroscopy of compounds equivalent to reevesite, formula (Ni,Co)₆Fe₂(OH)₁₆(CO₃)·4H₂O, with the ratio of Ni/Co ranging from 0 to 1, have been synthesised and characterised based on the molecular structure of the synthesised mineral. The combination of Raman spectroscopy with infrared spectroscopy enables an assessment of bands attributable to water stretching and brucite‐like surface hydroxyl units to be obtained. Raman spectroscopy shows a reduction in the symmetry of the carbonate anion, leading to the conclusion that the carbonate anion is bonded to the brucite‐like hydroxyl surface and to the water in the interlayer. Variation in the position of the carbonate anion stretching vibrations occurs and is dependent on the Ni/Co ratio. Water bending modes are identified in both the Raman and infrared spectra at positions greater than 1620 cm⁻¹, indicating that water is strongly hydrogen bonded to both the interlayer anions and the hydrotalcite surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopy of hydrogen‐arsenate group (AsO3OH) in solid‐state compounds: copper mineral phase geminite Cu(AsO3OH)·H2O from different geological environments

The participation of hydrogen‐arsenate group (AsO₃OH)²⁻ in solid‐state compounds may serve as a model example for explaining and clarifying the behaviour of As and other elements during weathering processes in natural environment. The mineral geminite, a hydrated hydrogen‐arsenate mineral of ideal formula Cu(AsO₃OH)·H₂O, has been studied by Raman and infrared spectroscopies. Two samples of geminite of different origin were investigated and the spectra proved quite similar. In the Raman spectra of geminite, six bands are observed at 741, 812, 836, 851, 859 and 885 cm⁻¹ (Salsigne, France), and 743, 813, 843, 853, 871 and 885 cm⁻¹ (Jáchymov, Czech Republic). The band at 851/853 cm⁻¹ is assigned to the ν₁ (AsO₃OH)²⁻ symmetric stretching mode; the other bands are assigned to the ν₃ (AsO₃OH)²⁻ split triply degenerate antisymmetric stretching mode. Raman bands at 309, 333, 345 and 364/310, 333 and 345 cm⁻¹ are attributed to the ν₂ (AsO₃OH)²⁻ bending mode, and a set of higher wavenumber bands (in the range 400–500 cm⁻¹) is assigned to the ν₄ (AsO₃OH)²⁻ split triply degenerate bending mode. A very complex set of overlapping bands is observed in both the Raman and infrared spectra. Raman bands are observed at 2289, 2433, 2737, 2855, 3235, 3377, 3449 and 3521/2288, 2438, 2814, 3152, 3314, 3448 and 3521 cm⁻¹. Two Raman bands at 2289 and 2433/2288 and 2438 cm⁻¹ are ascribed to the strong hydrogen bonded water molecules. The Raman bands at 3235, 3305 and 3377/3152 and 3314 cm⁻¹ may be assigned to the ν OH stretching vibrations of water molecules. Two bands at 3449 and 3521/3448 and 3521 cm⁻¹ are assigned to the OH stretching vibrations of the (AsO₃OH)²⁻ units. The lengths of the O H···O hydrogen bonds vary in the range 2.60–2.94 Å (Raman) and 2.61–3.07 Å (infrared). Two Raman and infrared bands in the region of the bending vibrations of the water molecules prove that structurally non‐equivalent water molecules are present in the crystal structure of geminite. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectrum of decrespignyite [(Y,REE)4Cu(CO3)4Cl(OH)5·2H2O] and its relation with those of other halogenated carbonates including bastnasite,hydroxybastnasite, parisite and northupite

Raman spectroscopy complemented with infrared spectroscopy has been used to study the rare‐earth‐based mineral decrespignyite [(Y,REE)₄Cu(CO₃)₄Cl(OH)₅· 2H₂O] and the spectrum compared with the Raman spectra of a series of selected natural halogenated carbonates from different origins including bastnasite, parisite and northupite. The Raman spectrum of decrespignyite displays three bands at 1056, 1070 and 1088 cm⁻¹ attributed to the CO₃²⁻ symmetric stretching vibration. The observation of three symmetric stretching vibrations is very unusual. The position of the CO₃²⁻ symmetric stretching vibration varies with the mineral composition. The Raman spectrum of decrespignyite shows bands at 1391, 1414, 1489 and 1547 cm⁻¹, whereas the Raman spectra of bastnasite, parisite and northupite show a single band at 1433, 1420 and 1554 cm⁻¹, respectively, assigned to the ν₃ (CO₃)²⁻ antisymmetric stretching mode. The observation of additional Raman bands for the ν₃ modes for some halogenated carbonates is significant in that it shows distortion of the carbonate anion in the mineral structure. Four Raman bands are observed at 791, 815, 837 and 849 cm⁻¹, which are assigned to the (CO₃)²⁻ν₂ bending modes. Raman bands are observed for decrespignyite at 694, 718 and 746 cm⁻¹ and are assigned to the (CO₃)²⁻ν₄ bending modes. Raman bands are observed for the carbonate ν₄ in‐phase bending modes at 722 cm⁻¹ for bastnasite, 736 and 684 cm⁻¹ for parisite and 714 cm⁻¹ for northupite. Multiple bands are observed in the OH stretching region for decrespignyite, bastnasite and parisite, indicating the presence of water and OH units in the mineral structure. Copyright © 2011 John Wiley & Sons, Ltd.     

Thermo‐Raman spectroscopy of synthetic nesquehonite — implication for the geosequestration of greenhouse gases

Pure nesquehonite (MgCO₃·3H₂O)/Mg(HCO₃)(OH)·2H₂O was synthesised and characterised by a combination of thermo‐Raman spectroscopy and thermogravimetry with evolved gas analysis. Thermo‐Raman spectroscopy shows an intense band at 1098 cm⁻¹, which shifts to 1105 cm⁻¹ at 450 °C, assigned to the ν₁CO₃²⁻ symmetric stretching mode. Two bands at 1419 and 1509 cm⁻¹ assigned to the ν₃ antisymmetric stretching mode shift to 1434 and 1504 cm⁻¹ at 175 °C. Two new peaks at 1385 and 1405 cm⁻¹ observed at temperatures higher than 175 °C are assigned to the antisymmetric stretching modes of the (HCO₃)⁻ units. Throughout all the thermo‐Raman spectra, a band at 3550 cm⁻¹ is attributed to the stretching vibration of OH units. Raman bands at 3124, 3295 and 3423 cm⁻¹ are assigned to water stretching vibrations. The intensity of these bands is lost by 175 °C. The Raman spectra were in harmony with the thermal analysis data. This research has defined the thermal stability of one of the hydrous carbonates, namely nesquehonite. Thermo‐Raman spectroscopy enables the thermal stability of the mineral nesquehonite to be defined, and, further, the changes in the formula of nesquehonite with temperature change can be defined. Indeed, Raman spectroscopy enables the formula of nesquehonite to be better defined as Mg(OH)(HCO₃)·2H₂O. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman and infrared study of phyllosilicates containing heavy metals (Sb,Bi): bismutoferrite and chapmanite

The kaolinite‐like phyllosilicate minerals bismutoferrite BiFe³⁺₂Si₂O₈(OH) and chapmanite SbFe³⁺₂Si₂O₈(OH) have been studied by Raman spectroscopy and complemented with infrared spectra. Tentatively interpreted spectra were related to their molecular structure. The antisymmetric and symmetric stretching vibrations of the Si O Si bridges, δ SiOSi and δ OSiO bending vibrations, ν (Si O_terminal)⁻ stretching vibrations, ν OH stretching vibrations of hydroxyl ions, and δ OH bending vibrations were attributed to the observed bands. Infrared bands in the range 3289–3470 cm⁻¹ and Raman bands in the range 1590–1667 cm⁻¹ were assigned to adsorbed water. O H···O hydrogen‐bond lengths were calculated from the Raman and infrared spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Transition of chromium oxyhydroxide nanomaterials to chromium oxide: a hot‐stage Raman spectroscopic study

The transition of disc‐like chromium hydroxide nanomaterials to chromium oxide nanomaterials has been studied by hot‐stage Raman spectroscopy. The structure and morphology of α‐CrO(OH) synthesised using hydrothermal treatment were confirmed by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The Raman spectrum of α‐CrO(OH) is characterised by two intense bands at 823 and 630 cm⁻¹ attributed to ν₁ Cr^III O symmetric stretching mode and the band at 1179 cm⁻¹ attributed to Cr^III OH δ deformation modes. No bands are observed above 3000 cm⁻¹. The absence of characteristic OH stretching vibrations may be due to short hydrogen bonds in the α‐CrO(OH) structure. Upon thermal treatment of α‐CrO(OH), new Raman bands are observed at 599, 542, 513, 396, 344 and 304 cm⁻¹, which are attributed to Cr₂O₃. This hot‐stage Raman study shows that the transition of α‐CrO(OH) to Cr₂O₃ occurs before 350 °C. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman spectroscopy of the borosilicate mineral ferroaxinite

Raman spectroscopy, complemented by infrared spectroscopy, has been used to characterise the ferroaxinite minerals of the theoretical formula Ca₂Fe²⁺Al₂BSi₄O₁₅(OH), a ferrous aluminium borosilicate. The Raman spectra are complex but are subdivided into sections on the basis of the vibrating units. The Raman spectra are interpreted in terms of the addition of borate and silicate spectra. Three characteristic bands of ferroaxinite are observed at 1082, 1056 and 1025 cm⁻¹ and are attributed to BO₄ stretching vibrations. Bands at 1003, 991, 980 and 963 cm⁻¹ are assigned to SiO₄ stretching vibrations. Bands are found in these positions for each of the ferroaxinites studied. No Raman bands were found above 1100 cm⁻¹ showing that ferroaxinites contain only tetrahedral boron. The hydroxyl stretching region of ferroaxinites is characterised by a single Raman band between 3368 and 3376 cm⁻¹, the position of which is sample‐dependent. Bands for ferroaxinite at 678, 643, 618, 609, 588, 572, 546 cm⁻¹ may be attributed to the ν₄ bending modes and the three bands at 484, 444 and 428 cm⁻¹ may be attributed to the ν₂ bending modes of the (SiO₄)²⁻. Copyright © 2006 John Wiley & Sons, Ltd.     

Raman spectroscopy of the joaquinite minerals

Selected joaquinite minerals have been studied by Raman spectroscopy. The minerals are categorised into two groups depending upon whether bands occur in the 3250 to 3450 cm⁻¹ region and in the 3450 to 3600 cm⁻¹ region, or in the latter region only. The first set of bands is attributed to water stretching vibrations and the second set to OH stretching bands. In the literature, X‐ray diffraction could not identify the presence of OH units in the structure of joaquinite. Raman spectroscopy proves that the joaquinite mineral group contains OH units in their structure, and in some cases both water and OH units. A series of bands at 1123, 1062, 1031, 971, 912 and 892 cm⁻¹ are assigned to SiO stretching vibrations. Bands above 1000 cm⁻¹ are attributable to the ν_as modes of the (SiO₄)⁴⁻ and (Si₂O₇)⁶⁻ units. Bands that are observed at 738, around 700, 682 and around 668, 621 and 602 cm⁻¹ are attributed to O Si O bending modes. The patterns do not appear to match the published infrared spectral patterns of either (SiO₄)⁴⁻ or (Si₂O₇)⁶⁻ units. The reason is attributed to the actual formulation of the joaquinite mineral, in which significant amounts of Ti or Nb and Fe are found. Copyright © 2007 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the magnesium‐carbonate minerals—artinite and dypingite

Magnesium minerals are important in the understanding of the concept of geosequestration. The two hydrated hydroxy magnesium‐carbonate minerals artinite and dypingite were studied by Raman spectroscopy. Intense bands are observed at 1092 cm⁻¹ for artinite and at 1120 cm⁻¹ for dypingite, attributed ν₁ symmetric stretching mode of CO₃²⁻. The ν₃ antisymmetric stretching vibrations of CO₃²⁻ are extremely weak and are observed at 1412 and 1465 cm⁻¹ for artinite and at 1366, 1447 and 1524 cm⁻¹ for dypingite. Very weak Raman bands at 790 cm⁻¹ for artinite and 800 cm⁻¹ for dypingite are assigned to the CO₃²⁻ν₂ out‐of‐plane bend. The Raman band at 700 cm⁻¹ of artinite and at 725 and 760 cm⁻¹ of dypingite are ascribed to CO₃²⁻ν₂ in‐plane bending mode. The Raman spectrum of artinite in the OH stretching region is characterised by two sets of bands: (1) an intense band at 3593 cm⁻¹ assigned to the MgOH stretching vibrations and (2) the broad profile of overlapping bands at 3030 and 3229 cm⁻¹ attributed to water stretching vibrations. X‐ray diffraction studies show that the minerals are disordered. This is reflected in the difficulty of obtaining Raman spectra of reasonable quality, and explains why the Raman spectra of these minerals have not been previously or sufficiently described. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman spectroscopy and characterisation of α‐gallium oxyhydroxide and β‐gallium oxide nanorods

Raman spectroscopy complemented by infrared spectroscopy was used to characterise both gallium oxyhydroxide (α‐GaO(OH)) and gallium oxide (β‐Ga₂O₃) nanorods synthesised with and without the surfactants using a soft chemical methodology at low temperatures. Nano‐ to micro‐sized gallium oxyhydroxide and gallium oxide materials were characterised and analysed by both X‐ray diffraction and Raman spectroscopy. Rod‐like GaO(OH) crystals with average length of ∼2.5 µm and width of 1.5 µm were obtained. Upon thermally treating gallium oxyhydroxide GaO(OH) to 900 °C, β‐Ga₂O₃ was synthesised retaining the initial GaO(OH) morphology. Raman spectroscopy has been used to study the structure of nanorods of GaO(OH) and Ga₂O₃ crystals. Raman spectroscopy shows bands characteristic of GaO(OH) at 950 and ∼1000 cm⁻¹ attributed to Ga OH deformation modes. Bands at 261, 275, 433 and 522 cm⁻¹ are assigned to vibrational modes involving Ga OH units. Bands observed at 320, 346, 418 and 472 cm⁻¹ are assigned to the deformation modes of Ga₂O₆ octahedra. Two sharp infrared bands at 2948 and 2916 cm⁻¹ are attributed to the GaO(OH) symmetric stretching vibrations. Raman spectroscopy of Ga₂O₃ provides bands at 630, 656 and 767 cm⁻¹ which are assigned to the bending and stretching of GaO₄ units. Raman bands at 417 and 475 cm⁻¹ are attributed to the symmetric stretching modes of GaO₂ units. The Raman bands at 319 and 347 cm⁻¹ are assigned to the bending modes of GaO₂ units. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and Raman spectroscopic characterisation of the oxalate mineral wheatleyite Na2Cu2+(C2O4)2·2H2O

The mineral wheatleyite has been synthesised and characterised by Raman spectroscopy complimented with infrared spectroscopy. Two Raman bands at 1434 and 1470 cm⁻¹ are assigned to the ν_{(C O)} stretching mode and implies two independent oxalate anions. Two intense Raman bands observed at 904 and 860 cm⁻¹ are assigned to the ν(C C) stretching mode and support the concept of two non‐equivalent oxalate units in the wheatleyite structure. Two strong bands observed at 565 and 585 cm⁻¹ are assigned to the symmetric CCO in plane bending modes. The Raman band at 387 cm⁻¹ is attributed to the CuO stretching vibration and the bands at 127 and 173 cm⁻¹ to OCuO bending vibrations. A comparison is made with Raman spectra of selected natural oxalate bearing minerals. Oxalates are markers or indicators of environmental events. Oxalates are readily determined by Raman spectroscopy. Thus, deterioration of works of art, biogeochemical cycles, plant metal complexation, the presence of pigments and minerals formed in caves can be analysed. Copyright © 2008 John Wiley & Sons, Ltd.     

A Raman spectroscopic study of the antimony mineral klebelsbergite Sb4O4(OH)2(SO4)

Many minerals based upon antimonite and antimonate anions remain to be studied. Most of the bands occur in the low wavenumber region, making the use of infrared spectroscopy difficult. This problem can be overcome by using Raman spectroscopy. The Raman spectra of the mineral klebelsbergite Sb₄O₄(OH)₂(SO₄) were studied and related to the structure of the mineral. The Raman band observed at 971 cm⁻¹ and a series of overlapping bands are observed at 1029, 1074, 1089, 1139 and 1142 cm⁻¹ are assigned to the SO₄²⁻ν₁ symmetric and ν₃ antisymmetric stretching modes, respectively. Two Raman bands are observed at 662 and 723 cm⁻¹, which are assigned to the Sb O ν₃ antisymmetric and ν₁ symmetric stretching modes, respectively. The intense Raman bands at 581, 604 and 611 cm⁻¹ are assigned to the ν₄ SO₄²⁻ bending modes. Two overlapping bands at 481 and 489 cm⁻¹ are assigned to the ν₂ SO₄²⁻ bending mode. Low‐intensity bands at 410, 435 and 446 cm⁻¹ may be attributed to O Sb O bending modes. The Raman band at 3435 cm⁻¹ is attributed to the O H stretching vibration of the OH units. Multiple Raman bands for both SO₄²⁻ and Sb O stretching vibrations support the concept of the non‐equivalence of these units in the klebelsbergite structure. It is proposed that the two sulfate anions are distorted to different extents in the klebelsbergite structure. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman spectroscopy of halogen‐containing carbonates

Raman spectroscopy complemented with infrared spectroscopy has been used to study a series of selected natural halogenated carbonates from different origins, including bastnasite, parisite and northupite. The position of CO₃²⁻ symmetric stretching vibration varies with the mineral composition. An additional band for northupite at 1107 cm⁻¹ is observed. Raman spectra of bastnasite, parisite and northupite show single bands at 1433, 1420 and 1554 cm⁻¹, respectively, assigned to the ν₃ (CO₃)²⁻ asymmetric stretching mode. The observation of additional Raman bands for the ν₃ modes for some halogenated carbonates is significant in that it shows distortion of the CaO₆ octahedron. No ν₂ Raman bending modes are observed for these minerals. The band is observed in the infrared spectra, and multiple ν₂ modes at 844 and 867 cm⁻¹ are observed for parisite. A single intense infrared band is found at 879 cm⁻¹ for northupite. Raman bands are observed forthe carbonate ν₄ in‐phase bending modes at 722 cm⁻¹ for bastnasite, 736 and 684 cm⁻¹ for parisite and 714 cm⁻¹ for northupite. Multiple bands are observed in the OH stretching region for selected bastansites and parisites, indicating the presence of water and OH units in the mineral structure. The presence of such bands brings into question the actual formula of these halogenated carbonate minerals. Copyright © 2007 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the multi‐anion mineral dixenite CuMn2+14Fe3+(AsO3)5(SiO4)2(AsO4)(OH)6

The mixed anion mineral dixenite has been studied by Raman spectroscopy, complemented with infrared spectroscopy. The Raman spectrum of dixenite shows bands at 839 and 813 cm⁻¹ assigned to the (AsO₃)³⁻ symmetric and antisymmetric stretching modes. The most intense Raman band of dixenite is the band at 526 cm⁻¹ and is assigned to the ν₂ AsO₃³⁻ bending mode. DFT calculations enabled the calculation of the position of AsO₂²⁻ symmetric stretching mode at 839 cm⁻¹, the antisymmetric stretching mode at 813 cm⁻¹, and the deformation mode at 449 cm⁻¹. The Raman bands at 1026 and 1057 cm⁻¹ are assigned to the SiO₄²⁻ symmetric stretching vibrations and those at 1349 and 1386 cm⁻¹ to the SiO₄²⁻ antisymmetric stretching vibrations. Both Raman and infrared spectra indicate the presence of water in the structure of dixenite. This brings into question the commonly accepted formula of dixenite as CuMn²⁺₁₄Fe³⁺(AsO₃)₅(SiO₄)₂(AsO₄)(OH)₆. The formula may be better written as CuMn²⁺₁₄Fe³⁺(AsO₃)₅(SiO₄)₂(AsO₄)(OH)₆·xH₂O. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the antimonate mineral lewisite (Ca,Fe, Na)2(Sb,Ti)2O6(O,OH)7

The mineral lewisite, (Ca, Fe, Na)₂(Sb, Ti)₂O₆(O, OH)₇, an antimony-bearing mineral, has been studied by Raman spectroscopy. A comparison is made with the Raman spectra of other minerals, including bindheimite, stibiconite, and roméite. The mineral lewisite is characterised by an intense sharp band at 517 cm^?1 with a shoulder at 507 cm^?1 assigned to SbO stretching modes. Raman bands of medium intensity for lewisite are observed at 300, 356, and 400 cm^?1. These bands are attributed to OSbO bending vibrations. Raman bands in the OH stretching region are observed at 3200, 3328, 3471 cm^?1, with a distinct shoulder at 3542 cm^?1. The latter is assigned to the stretching vibration of OH units. The first three bands are attributed to water stretching vibrations. The observation of bands in the 3200–3500 cm^?1 region suggests that water is involved in the lewisite structure. If this is the case then the formula may be better written as (Ca, Fe²⁺, Na)₂(Sb, Ti)₂(O, OH)₇ xH₂O.