Eloise C. Keeffe

Raman spectroscopic study of a hydroxy-arsenate mineral containing bismuth-atelestite Bi2O(OH)(AsO4)

The Raman spectrum of atelestite Bi2O(OH)(AsO4), a hydroxy-arsenate mineral containing bismuth, has been studied in terms of spectra-structure relations. The studied spectrum is compared with the Raman spectrum of atelestite downloaded from the RRUFF database. The sharp intense band at 834 cm(-1) is assigned to the ν1 AsO4(3-) (A1) symmetric stretching mode and the three bands at 767, 782 and 802 cm(-1) to the ν3 AsO4(3-) antisymmetric stretching modes. The bands at 310, 324, 353, 370, 395, 450, 480 and 623 cm(-1) are assigned to the corresponding ν4 and ν2 bending modes and BiOBi (vibration of bridging oxygen) and BiO (vibration of non-bridging oxygen) stretching vibrations. Lattice modes are observed at 172, 199 and 218 cm(-1). A broad low intensity band at 3095 cm(-1) is attributed to the hydrogen bonded OH units in the atelestite structure. A weak band at 1082 cm(-1) is assigned to δ(BiOH) vibration.

Structure of selected basic zinc/copper (II) phosphate minerals based upon near-infrared spectroscopy : implications for hydrogen bonding

The NIR spectra of reichenbachite, scholzite and parascholzite have been studied at 298 K. The spectra of the minerals are different, in line with composition and crystal structural variations. Cation substitution effects are significant in their electronic spectra and three distinctly different electronic transition bands are observed in the near-infrared spectra at high wavenumbers in the 12,000-7600 cm(-1) spectral region. Reichenbachite electronic spectrum is characterised by Cu(II) transition bands at 9755 and 7520 cm(-1). A broad spectral feature observed for ferrous ion in the 12,000-9000 cm(-1) region both in scholzite and parascholzite. Some what similarities in the vibrational spectra of the three phosphate minerals are observed particularly in the OH stretching region. The observation of strong band at 5090 cm(-1) indicates strong hydrogen bonding in the structure of the dimorphs, scholzite and parascholzite. The three phosphates exhibit overlapping bands in the 4800-4000 cm(-1) region resulting from the combinations of vibrational modes of (PO(4))(3-) units.

The mixed anion mineral parnauite Cu9[(OH)10|SO4|(AsO4)2]·7H2O—A Raman spectroscopic study

The mixed anion mineral parnauite Cu(9)[(OH)(10)|SO(4)|(AsO(4))(2)]·7H(2)O from two localities namely Cap Garonne Mine, Le Pradet, France and Majuba Hill mine, Pershing County, Nevada, USA has been studied by Raman spectroscopy. The Raman spectrum of the French sample is dominated by an intense band at 975 cm(-1) assigned to the ν(1) (SO(4))(2-) symmetric stretching mode and Raman bands at 1077 and 1097 cm(-1) may be attributed to the ν(3) (SO(4))(2-) antisymmetric stretching mode. Two Raman bands 1107 and 1126 cm(-1) are assigned to carbonate CO(3)(2-) symmetric stretching bands and confirms the presence of carbonate in the structure of parnauite. The comparatively sharp band for the Pershing County mineral at 976 cm(-1) is assigned to the ν(1) (SO(4))(2-) symmetric stretching mode and a broad spectral profile centered upon 1097 cm(-1) is attributed to the ν(3) (SO(4))(2-) antisymmetric stretching mode. Two intense bands for the Pershing County mineral at 851 and 810 cm(-1) are assigned to the ν(1) (AsO(4))(3-) symmetric stretching and ν(3) (AsO(4))(3-) antisymmetric stretching modes. Two Raman bands for the French mineral observed at 725 and 777 cm(-1) are attributed to the ν(3) (AsO(4))(3-) antisymmetric stretching mode. For the French mineral, a low intensity Raman band is observed at 869 cm(-1) and is assigned to the ν(1) (AsO(4))(3-) symmetric stretching vibration. Chemical composition of parnauite remains open and the question may be raised is parnauite a solid solution of two or more minerals such as a copper hydroxy-arsenate and a copper hydroxy sulphate.

An application of near infrared spectroscopy to the study of the selenite minerals: chalcomenite, clinochalcomenite and cobaltomenite

The selection of five naturally occurring selenite minerals that contain two different transition metal ions, Cu2+ and Co2+ could be distinguished by near infrared spectroscopy. Dependence of composition on spectral properties is a key to mineral identification and differentiation of the members of the selenite group. The nature of the band positions and splitting of band components in the electronic spectra of Cu2+ selenites in the region 12,400–8000 cm−1 are in conformity with octahedral geometry distortion. The two split components which are observed for the Co2+ band near 9000 cm−1 in cobaltomenites are considered as the vibrational satellites of spin-allowed transition 4T1g(F)→4T2g(F). Bands observed at 6950 cm−1, 6810 cm−1 and 6700 cm−1 are the overtones of OH stretches of structural water in selenites and a strong absorption feature near 6700 cm−1 is the result of hydrogen bonding between (SeO3)2– and H2O. These bands are shifted in cobaltomenites. A sharp absorption band at 5170 cm−1 is a common feature in all the spectra of selenite minerals and is the contribution by the combinations of the OH vibrations of water molecules, ν3 and ν1. A series of overlapping bands around 4500 and 4100 cm−1 is the result of the combination of the vibrational modes of (SeO3)2– ion in the minerals.

An application of near-infrared and mid-infrared spectroscopy to the study of selected minerals

Near-infrared (NIR) spectroscopy is a somewhat underutilised technique for the study of minerals. The technique has the ability to determine water content, hydroxyl groups and transition metals. In this paper, we show the application of NIR spectroscopy to the study of selected minerals. The structure and spectral properties of two Cu-tellurite minerals graemite and teineite are compared with bismuth containing tellurite mineral smirnite by the application of NIR and infrared (IR) spectroscopy. The position of Cu2+ bands and their splitting in the electronic spectra of tellurites are in conformity with the octahedral geometry distortion. The spectral pattern of smirnite resembles graemite and the observed band at 10,855 cm−1 with a weak shoulder at 7920 cm−1 is identified as due to a Cu2+ ion. Any transition metal impurities may be identified by their bands in this spectral region. Three prominent bands observed in the region of 7200–6500 cm−1 are the overtones of water while the weak bands observed near 6200 cm−1 in tellurites may be attributed to the hydrogen bonding between (TeO3)2− and H2O. The observation of a number of bands centred at around 7200 cm−1 confirms molecular water in tellurite minerals. A number of overlapping bands in the low wavenumbers 4500–4000 cm−1 is the result of combinational modes of (TeO3)2− ion. The appearance of the most intense peak at 5200 cm−1 with a pair of weak bands near 6000 cm−1 is a common feature in all the spectra and is related to the combinations of OH vibrations of water molecules and bending vibrations ν2 (δ H2O). Bending vibrations δ H2O observed in the IR spectra show a single band for smirnite at 1610 cm−1. The resolution of this band into a number of components is evidenced for non-equivalent types of molecular water in graemite and teineite. (TeO3)2− stretching vibrations are characterised by three main absorptions at 1080, 780 and 695 cm−1.

An application of near infrared and mid-infrared spectroscopy to the study of natural halotrichites: halotrichite, apjohnite and wupatkiite

Near infrared (NIR) and Fourier transform infrared (FT-IR) spectroscopy have been used to determine the mineralogical character of isomorphic substitutions for Mg2* by divalent transition metals Fe, Mn, Co and Ni in natural halotrichite series. The minerals are characterised by d→d transitions in the NIR region 12,000–7500 cm−1. The NIR spectrum of halotrichite reveals broad features from 12,000 cm−1 to 7500 cm−1 with a splitting of two bands resulting from ferrous ion transition 5T2g→5Eg. The presence of overtones of OH− fundamentals near 7000 cm−1 confirms molecular water in the mineral structure of the halotrichite series. The appearance of the most intense peak at around 5132 cm−1 is a common feature in the three minerals and is derived from a combination of OH− vibrations of water molecules and v2 water-bending modes. The influence of cations such as Mg2+, Fe2+, Mn2+, Co2+ and Ni2+ shows on the spectra of halotrichites, especially for wupatkiite-OH stretching vibrations in which bands are distorted conspicuously to low wave numbers at 3270 cm−1, 2904 cm−1 and 2454 cm−1. The observation of a high-frequency v2 mode in the infrared spectrum at 1640 cm−1 indicates that the coordination of water molecules is strongly hydrogen bonded in natural halotrichites. The splitting of bands in v3 and v4 (SO4)2− stretching regions may be attributed to the reduction of symmetry from T d to C2v for sulphate ion. This work has shown the usefulness of NIR spectroscopy for the rapid identification and classification of the halotrichite minerals.

Raman spectroscopic study of the tellurite minerals : Carlfriesite and spiroffite

Raman spectroscopy has been used to study the tellurite minerals spiroffite and carlfriesite, which are minerals of formula type A(2)(X(3)O(8)) where A is Ca(2+) for the mineral carlfriesite and is Zn(2+) and Mn(2+) for the mineral spiroffite. Raman bands for spiroffite observed at 721 and 743 cm(-1), and 650 cm(-1) are attributed to the nu(1) (Te(3)O(8))(2-) symmetric stretching mode and the nu(3) (Te(3)O(8))(2-) antisymmetric stretching modes, respectively. A second spiroffite mineral sample provided a Raman spectrum with bands at 727 cm(-1) assigned to the nu(1) (Te(3)O(8))(2-) symmetric stretching modes and the band at 640cm(-1) accounted for by the nu(3) (Te(3)O(8))(2-) antisymmetric stretching mode. The Raman spectrum of carlfriesite showed an intense band at 721 cm(-1). Raman bands for spiroffite, observed at (346, 394) and 466 cm(-1) are assigned to the (Te(3)O(8))(2-)nu(2) (A(1)) bending mode and nu(4) (E) bending modes. The Raman spectroscopy of the minerals carlfriesite and spiroffite are difficult because of the presence of impurities and other diagenetically related tellurite minerals.

A Raman spectroscopic study of the antimonite mineral peretaite Ca(SbO)4(OH)2(SO4)2•2H2O

Raman spectra of mineral peretaite Ca(SbO)(4)(OH)(2)(SO(4))(2).2H(2)O were studied, and related to the structure of the mineral. Raman bands observed at 978 and 980cm(-1) and a series of overlapping bands observed at 1060, 1092, 1115, 1142 and 1152cm(-1) are assigned to the SO(4)(2-)nu(1) symmetric and nu(3) antisymmetric stretching modes. Raman bands at 589 and 595cm(-1) are attributed to the SbO symmetric stretching vibrations. The low intensity Raman bands at 650 and 710cm(-1) may be attributed to SbO antisymmetric stretching modes. Raman bands at 610cm(-1) and at 417, 434 and 482cm(-1) are assigned to the SO(4)(2-)nu(4) and nu(2) bending modes, respectively. Raman bands at 337 and 373cm(-1) are assigned to O-Sb-O bending modes. Multiple Raman bands for both SO(4)(2-) and SbO stretching vibrations support the concept of the non-equivalence of these units in the peretaite structure.

Spectroscopy of selected copper group minerals : chalcophyllite and chenevixite-implications for hydrogen bonding

NIR and IR spectroscopy has been applied for detection of chemical species and the nature of hydrogen bonding in arsenate complexes. The structure and spectral properties of copper(II) arsenate minerals: chalcophyllite and chenevixite are compared with copper(II) sulphate minerals: devilline, chalcoalumite and caledonite. Split NIR bands in the electronic spectrum of two ranges 11,700-8500 cm(-1) and 8500-7200 m(-1) confirm distortion of octahedral symmetry for Cu(II) in the arsenate complexes. The observed bands with maxima at 9860 and 7750 cm(-1) are assigned to Cu(II) transitions (2)B(1g)-->(2)B(2g) and (2)B(1g)-->(2)A(1g). Overlapping bands in the NIR region 4500-4000 cm(-1) is the effect of multi-anions OH(-), (AsO(4))(3-) and (SO(4))(2-). The observation of broad and diffuse bands in the range 3700-2900 cm(-1) confirms strong hydrogen bonding in chalcophyllite relative to chenevixite. The position of the water bending vibrations indicates the water is strongly hydrogen bonded in the mineral structure. The strong absorption feature centred at 1644 cm(-1) in chalcophyllite indicates water is strongly hydrogen bonded in the mineral structure. The H(2)O-bending vibrations shift to low wavenumbers in chenevixite and an additional band observed at 1390 cm(-1) is related to carbonate impurity. The characterisation of IR spectra by nu(3) antisymmetric stretching vibrations of (SO(4))(2-) and (AsO(4))(3) ions near 1100 and 800 cm(-1) respectively is the result of isomorphic substitution for arsenate by sulphate in both the minerals of chalcophyllite and chenevixite.

Characterisation of the copper arsenate mineral strashimirite, Cu8(AsO4)4(OH)4·4H2O, by near infrared spectroscopy

Near infrared (NIR) spectra of the strashimirite minerals from two different origins have been investigated. The structure and spectral properties of a copper-bearing arsenate mineral are compared. Two prominent bands observed at 11,187 cm−1 and 8443 cm−1 (Czech) and 11327 cm−1 and 8732 cm−1 (Slovak) are assigned to 2B1g→2B2g and 2B1g→2A1g transitions of Cu2+ ion in strashimirite. Intense bands at 7247 cm−1 and 6800 cm−1 are attributed to the first overtone of the water and OH fundamentals observed in a complex spectral profile centred upon 3300 cm−1. The very broad NIR band at 5150 cm−1 is assigned to combination bands of water and OH vibrations. Bands in the 4800 cm−1 to 4000 cm−1 are assigned to (AsO4)3− combination bands.