Raman spectroscopic study of the mixed anion sulphate–arsenate mineral parnauite Cu9[(OH)10|SO4|(AsO4)2]·7H2O

The mixed anion mineral parnauite Cu₉[(OH)₁₀|SO₄|(AsO₄)₂]·7H₂O has been studied by Raman spectroscopy. Characteristic bands associated with arsenate, sulphate and hydroxyl units are identified. Broad bands are observed and are resolved into component bands. Two intense bands at 859 and 830 cm⁻¹ are assigned to the ν₁ (AsO₄)³⁻ symmetric stretching and ν₃ (AsO₄)³⁻ antisymmetric stretching modes. The comparatively sharp band at 976 cm⁻¹ is assigned to the ν₁ (SO₄)²⁻ symmetric stretching mode and a broad‐spectral profile centered upon 1097 cm⁻¹ is attributed to the ν₃ (SO₄)²⁻ antisymmetric stretching mode. A comparison of the Raman spectra is made with other arsenate‐bearing minerals such as carminite, clinotyrolite, kankite, tilasite and pharmacosiderite. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the hydroxy‐arsenate‐sulfate mineral chalcophyllite Cu18Al2(AsO4)4(SO4)3(OH)24·36H2O

The mixed anion mineral chalcophyllite Cu₁₈Al₂(AsO₄)₄(SO₄)₃(OH)₂₄·36H₂O has been studied by using Raman and infrared spectroscopies. Characteristic bands associated with arsenate, sulfate and hydroxyl units are identified. Broad bands in the OH stretching region are observed and are resolved into component bands. Estimates of hydrogen bond distances were made using a Libowitzky function. Both short and long hydrogen bonds were identified. Two intense bands at 841 and ∼814 cm⁻¹ are assigned to the ν₁ (AsO₄)³⁻ symmetric stretching and ν₃ (AsO₄)³⁻ antisymmetric stretching modes. The comparatively sharp band at 980 cm⁻¹ is assigned to the ν₁ (SO₄)²⁻ symmetric stretching mode, and a broad spectral profile centred upon 1100 cm⁻¹ is attributed to the ν₃ (SO₄)²⁻ antisymmetric stretching mode. A comparison of the Raman spectra is made with other arsenate‐bearing minerals such as carminite, clinotyrolite, kankite, tilasite and pharmacosiderite. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman microscopy of haidingerite Ca(AsO3OH)·H2O and brassite Mg(AsO3OH)·4H2O

Raman spectroscopy has been used to study the arsenate minerals haidingerite Ca(AsO₃OH)·H₂O and brassite Mg(AsO₃OH)·4H₂O. Intense Raman bands in the haidingerite spectrum observed at 745 and 855 cm⁻¹ are assigned to the (AsO₃OH)²⁻ν₃ antisymmetric stretching and ν₁ symmetric stretching vibrational modes. For brassite, two similarly assigned intense bands are found at 809 and 862 cm⁻¹. The observation of multiple Raman bands in the (AsO₃OH)²⁻ stretching and bending regions suggests that the arsenate tetrahedrons in the crystal structures of both minerals studied are strongly distorted. Broad Raman bands observed at 2842 cm⁻¹ for haidingerite and 3035 cm⁻¹ for brassite indicate strong hydrogen bonding of water molecules in the structure of these minerals. OH···O hydrogen‐bond lengths were calculated from the Raman spectra based on empirical relations. Copyright © 2009 John Wiley & Sons, Ltd.     

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.     

A Raman spectroscopic study of bukovskýite Fe2(AsO4)(SO4)(OH)· 7H2O,a mineral phase with a significant role in arsenic migration

The Raman spectrum of bukovskýite [Fe³⁺₂(OH)(SO₄)(AsO₄)· 7H₂O] has been studied and compared with that of an amorphous gel containing specifically Fe, As and S, which is understood to be an intermediate product in the formation of bukovskýite. The observed bands are assigned to the stretching and bending vibrations of (SO₄)²⁻ and (AsO₄)³⁻ units, stretching and bending vibrations and vibrational modes of hydrogen‐bonded water molecules, stretching and bending vibrations of hydrogen‐bonded (OH)⁻ ions and Fe³⁺ (O,OH) units. The approximate range of O H···O hydrogen bond lengths was inferred from the Raman spectra. Raman spectra of crystalline bukovskýite and of the amorphous gel differ in that the bukovskýite spectrum is more complex, the observed bands are sharp and the degenerate bands of (SO₄)²⁻ and (AsO₄)³⁻ are split and more intense. Lower wavenumbers of δ H₂O bending vibrations in the spectrum of the amorphous gel may indicate the presence of weaker hydrogen bonds compared to those in bukovskýite. Copyright © 2011 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 spectroscopy of hydrogen‐arsenate group (AsO3OH) in solid‐state compounds: cobalt mineral phase burgessite Co2(H2O)4[AsO3OH]2·H2O

Raman spectrum of burgessite, Co₂(H₂O)₄[AsO₃OH]₂· H₂O, was studied, interpreted and compared with its infrared spectrum. The stretching and bending vibrations of (AsO₃) and As‐OH units, as well as the stretching, bending and libration modes of water molecules and hydroxyl ions were assigned. The range of O H···O hydrogen bond lengths was inferred from the Raman and infrared spectra of burgessite. The presence of (AsO₃OH)²⁻ units in the crystal structure of burgessite was proved, which is in agreement with its recently solved crystal structure. Raman and infrared spectra of erythrite inferred from the RRUFF database are used for comparison. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman spectroscopy of hydrogen arsenate group (AsO3OH)2− in solid‐state compounds: cobalt‐containing zinc arsenate mineral,koritnigite (Zn,Co)(AsO3OH)·H2O

Raman spectra of two well‐defined types of koritnigite crystals from the Jáchymov ore district, Czech Republic, were recorded and interpreted. No substantial differences were observed between both crystal types. The observed Raman bands were attributed to the (AsO₃OH)²⁻ stretching and bending vibrations as well as stretching and bending vibrations of water molecules and hydroxyl ions. The non‐interpreted Raman spectra of koritnigite from the RRUFF database and the published infrared spectra of cobaltkoritnigite were used for comparison. The O H···O hydrogen bond lengths in the crystal structure of koritnigite were inferred from the Raman spectra and compared with those derived from the X‐ray single‐crystal refinement. The presence of (AsO₃OH)²⁻ units in the crystal structure of koritnigite was proved from the Raman spectra, which supports the conclusions of the X‐ray structure analysis. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the uranyl mineral metauranospinite Ca[(UO2)(AsO4)]2·8H2O

Raman spectra of metauranospinite Ca[(UO₂)(AsO₄)]₂·8H₂O complemented with infrared spectra were studied. Observed bands were assigned to the stretching and bending vibrations of (UO₂)²⁺ and (AsO₄)³⁻ units and of water molecules. U O bond lengths in uranyl and O H···O hydrogen bond lengths were calculated from the Raman and infrared spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman microscopy of the mixite mineral BiCu6(AsO4)3(OH)6·3H2O from the Czech Republic

Raman microscopy of the mixite mineral BiCu₆(AsO₄)₃(OH)₆·3H₂O from Jáchymov and from Smrkovec (both Czech Republic) has been used to study their molecular structure. The presence of (AsO₄)³⁻, (AsO₃OH)²⁻, (PO₄)³⁻ and (PO₃OH)²⁻ units, as well as molecular water and hydroxyl ions, was inferred. O H···O hydrogen bond lengths were calculated from the Raman and infrared spectra using Libowitzky's empirical relation. Small differences in the Raman spectra between both samples were observed and attributed to compositional and hydrogen‐bonding network differences. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the hydrogen and arsenate bonding environment in isostructural synthetic arsenates of the variscite group—M3+ AsO4·2H2O (M3+ = Fe,Al, In and Ga): implications for arsenic release in water

The Raman spectra of synthetic compounds equivalent to the variscite group: FeAsO₄·2H₂O AlAsO₄·2H₂O, GaAsO₄·2H₂O, and InAsO₄·2H₂O are reported. In particular, upon comparison of FeAsO₄·2H₂O to AlAsO₄·2H₂O, it is observed that the Type II (weak) H‐bond lengths in the latter are slightly longer, which is postulated to affect the stability (As release) in water at pH 5 and 7. Arsenate stretching and bending vibrations were found to be distinct in terms of spectral structure and therefore well suited for fingerprinting. The calculated As O bond strengths from existing crystallographic data showed no significant variations. The strongest ν₁ (AsO₄³⁻) stretch was used to monitor the As O bonding interactions in the four As O M units, where a shift of 114 cm⁻¹ was observed in the order FeAsO₄·2H₂O (lowest) < InAsO₄·2H₂O < GaAsO₄·2H₂O < AlAsO₄·2H₂O (highest); this order also followed exactly the measured arsenic release of these phases. This shift in ν₁ (AsO₄³⁻) position was rationalized to stem from the differences in the electronegativities of the M³⁺ cations. The trends mentioned above were verified and found to also hold for the isostructural phosphate analogues strengite (FePO₄·2H₂O) and variscite (AlPO₄·2H₂O) using published data. Therefore, it is postulated that, as observed with the stability of solution complexes, there may be a correlation between the electronegativity of the M³⁺ cation in these isostructural phases and their stability (As or P release) in water. Copyright © 2010 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 the uranyl mineral natrouranospinite (Na2,Ca)[(UO2)(AsO4)]2· 5H2O

Raman spectra of natrouranospinite complemented with infrared spectra were studied and related to the structure of the mineral. Observed bands were assigned to the stretching and bending vibrations of (UO₂)²⁺ and (AsO₄)³⁻ units and of water molecules. U O bond lengths in uranyl and O H···O hydrogen bond lengths were calculated from the Raman and infrared spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the phosphate mineral churchite‐(Y) YPO4·2H2O

Raman spectroscopy has been used to study the rare‐earth mineral churchite‐(Y) of formula (Y,REE)(PO₄) ·2H₂O, where rare‐earth element (REE) is a rare‐earth element. The mineral contains yttrium and, depending on the locality, a range of rare‐earth metals. The Raman spectra of two churchite‐(Y) mineral samples from Jáchymov and Medvědín in the Czech Republic were compared with the Raman spectra of churchite‐(Y) downloaded from the RRUFF data base. The Raman spectra of churchite‐(Y) are characterized by an intense sharp band at 975 cm⁻¹ assigned to the ν₁ (PO₄³⁻) symmetric stretching mode. A lower intensity band observed at around 1065 cm⁻¹ is attributed to the ν₃ (PO₄³⁻) antisymmetric stretching mode. The (PO₄³⁻) bending modes are observed at 497 cm⁻¹ (ν₂) and 563 cm⁻¹ (ν₄). Some small differences in the band positions between the four churchite‐(Y) samples from four different localities were found. These differences may be ascribed to the different compositions of the churchite‐(Y) minerals. Copyright © 2009 John Wiley & Sons, Ltd.     

A Raman spectroscopic study of copiapites Fe2+Fe3+(SO4)6(OH)2 · 20H2O: environmental implications

Raman spectroscopy has been used to study selected mineral samples of the copiapite group. Copiapite (Fe²⁺Fe³⁺(SO₄)₆(OH)₂ · 20H₂O) is a secondary mineral formed through the oxidation of pyrite. Minerals of the copiapite group have the general formula AFe₄(SO₄)₆(OH)₂ · 20H₂O, where A has a + 2 charge and can be either magnesium, iron, copper, calcium and/or zinc. The formula can also be B_2/3Fe₄(SO₄)₆(OH)₂ · 20H₂O, where B has a + 3 charge and may be either aluminium or iron. For each mineral, two Raman bands are observed at around 992 and 1029 cm⁻¹, assigned to the (SO₄)²⁻ν₁ symmetric stretching mode. The observation of two bands provides evidence for the existence of two non‐equivalent sulfate anions in the mineral structure. Three Raman bands at 1112, 1142 and 1161 cm⁻¹ are observed in the Raman spectrum of copiapites, indicating a reduction of symmetry of the sulfate anion in the copiapite structure. This reduction in symmetry is supported by multiple bands in the ν₂ and ν₄(SO₄)²⁻ spectral regions. Copyright © 2010 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 uranyl mineral pseudojohannite Cu6.5[(UO2)4O4(SO4)2]2(OH)5·25H2O

Raman spectra of pseudojohannite were studied and related to the structure of the mineral. Observed bands were assigned to the stretching and bending vibrations of (UO₂)²⁺ and (SO₄)²⁻ units and of water molecules. The published formula of pseudojohannite is Cu_6.5(UO₂)₈[O₈](OH)₅[(SO₄)₄]·25H₂O. Raman bands at 805 and 810 cm⁻¹ are assigned to (UO₂)²⁺ stretching modes. The Raman bands at 1017 and 1100 cm⁻¹ are assigned to the (SO₄)²⁻ symmetric and antisymmetric stretching vibrations. The three Raman bands at 423, 465 and 496 cm⁻¹ are assigned to the (SO₄)²⁻ν₂ bending modes. The bands at 210 and 279 cm⁻¹ are assigned to the doubly degenerate ν₂ bending vibration of the (UO₂)²⁺ units. U O bond lengths in uranyl and O H···O hydrogen bond lengths were calculated from the Raman and infrared spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the arsenite minerals leiteite ZnAs2O4, reinerite Zn3(AsO3)2 and cafarsite Ca5(Ti,Fe,Mn)7(AsO3)12·4H2O

The selected arsenite minerals leiteite, reinerite and cafarsite have been studied by Raman spectroscopy. Density functional theory (DFT) calculations enabled the position of the AsO₂²⁻ symmetric stretching mode at 839 cm⁻¹, the antisymmetric stretching mode at 813 cm⁻¹ and the deformation mode at 449 cm⁻¹ to be calculated. The Raman spectrum of leiteite shows bands at 804 and 763 cm⁻¹ assigned to the As₂O₄²⁻ symmetric and antisymmetric stretching modes. The most intense Raman band of leiteite is the band at 457 cm⁻¹ and is assigned to the ν₂ As₂O₄²⁻ bending mode. A comparison of the Raman spectrum of leiteite is made with the arsenite minerals reinerite and cafarsite. Copyright © 2009 John Wiley & Sons, Ltd.     

A Raman spectroscopic study of the ‘cave’ mineral ardealite Ca2(HPO4)(SO4)·4H2O

The mineral ardealite Ca₂(HPO₄)(SO₄)·4H₂O is a ‘cave’ mineral and is formed through the reaction of calcite with bat guano. The mineral shows disorder and the composition varies depending on the origin of the mineral. Raman spectroscopy complimented with infrared spectroscopy has been used to characterise the mineral ardealite. The Raman spectrum is very different from that of gypsum. Bands are assigned to SO₄²⁻ and HPO₄²⁻ stretching and bending modes. Copyright © 2011 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the uranyl sulphate mineral jáchymovite (UO2)8(SO4)(OH)14· 13H2O

Raman spectra of jáchymovite, (UO₂)₈(SO₄)(OH)₁₄·13H₂O, were studied, complemented with infrared spectra, and compared with published Raman and infrared spectra of uranopilite, [(UO₂)₆(SO₄)O₂(OH)₆(H₂O)₆]·6H₂O. Bands related to the stretching and bending vibrations of (UO₂)²⁺, (SO₄)²⁻, (OH)⁻ and water molecules were assigned. U O bond lengths in uranyl and O H· · ·O hydrogen bond lengths were calculated from the Raman and infrared spectra. Copyright © 2009 John Wiley & Sons, Ltd.