Vibrational spectroscopic study of the mineral penkvilksite Na2TiSi4O11·2H2O – a mineral used for the uptake of radionuclides

We have used vibrational spectroscopy to study the formula and molecular structure of the mineral penkvilksite Na 2TiSi 4O 11·2H 2O. Penkvilksite is a mineral which may be used in the uptake of radioactive elements. Both Raman and infrared spectroscopies identify a band at 3638 cm−1 attributed to an OH-stretching vibration of hydroxyl units. The inference is that OH units are involved in the structure of penkvilksite. The formula may be well written as Na 2TiSi 4O 10(OH)2·H 2O. The mineral is characterised by a very intense Raman band at 1085 cm−1 and a broad infrared band at 1080 cm−1 assigned to SiO-stretching vibrations. Raman bands at 620, 667 and 711 cm−1 are attributed to SiO and TiO chain bonds. Water-stretching vibrations are observed as Raman bands at 3197, 3265, 3425 and 3565 cm−1. Vibrational spectroscopy enables aspects of the molecular structure of the mineral penkvilksite to be ascertained. Penkvilksite is a mineral which can incorporate actinides and lanthanides from radioactive waste.

Vibrational spectroscopy of natural cave mineral monetite CaHPO4 and the synthetic analog

Monetite is a phosphate mineral formed by the reaction of the chemicals in bat guano with calcite substrates and is commonly found in caves. The analog of the mineral monetite CaHPO4 has been synthesized and the Raman and infrared spectra of the natural monetite originating from the Murra-el-elevyn Cave, Eucla, Western Australia, compared. Monetite is characterized by a complex set of phosphate bands that arise because of two sets of pairs of phosphate units in the unit cell. Raman and infrared bands are assigned to HPO4(2-), OH stretching and bending vibrations. Infrared bands at 1346 and 1402 cm−1 are assigned to POH deformation modes. Vibrational spectroscopy confirms the presence of monetite in the cave system.

The phosphate mineral sigloite Fe3+Al2(PO4)2(OH)3·7(H2O), an exception to the paragenesis rule – a vibrational spectroscopic study

The secondary phosphate mineral sigloite Fe3+Al2(PO4)2(OH)3·7H2O is the exception to the rule that phosphate mineral paragenesis is related to the final phase of hydrothermal mineralization at low temperatures. Sigloite was formed as an oxidation pseudomorph after paravauxite, during the last supergene paragenetic stage. We have studied the secondary phosphate mineral sigloite Fe3+Al2(PO4)2(OH)3·7H2O using vibrational spectroscopic techniques. Because the mineral is a phosphate mineral, it is readily studied by spectroscopic techniques as the phosphate and hydrogen phosphate units are readily measured. Indeed, sigloite shows the presence of both phosphate and hydrogen phosphate units in its structure. Raman bands at 1009 cm−1 with shoulders at 993 and 1039 cm−1 are assigned to stretching vibrations of and units. The Raman band at 993 cm−1 is assigned to the ν1 symmetric stretching mode of the POH units, whereas the Raman band at 1009 cm−1 is assigned to the ν1 symmetric stretching mode. Raman bands observed at 506, 528, 571, 596, 619 and 659 cm−1 are attributed to the ν4 out of plane bending modes of the PO4 and H2PO4 units. The Raman bands at 2988, 3118 and 3357 cm−1 are assigned to water stretching vibration. The series of bands at 3422, 3449, 3493, 3552 and 3615 cm−1 are assigned to the OH stretching vibrations of the hydroxyl units. The observation of multiple bands gives credence to the non-equivalence of the OH units in the sigloite structure.

The mineral tooeleite Fe6(AsO3)4SO4(OH)4⋅4H2O – An infrared and Raman spectroscopic study-environmental implications for arsenic remediation

The mineral tooeleite Fe6(AsO3)4SO4(OH)4�4H2O is secondary ferric arsenite sulphate mineral which has environmental significance for arsenic remediation because of its high stability in the regolith. The mineral has been studied by X-ray diffraction (XRD), infrared (IR) and Raman spectroscopy. The XRD result indicates tooeleite can form more crystalline solids in an acid environment than in an alkaline environment. Infrared spectroscopy identifies moderately intense band at 773 cm�1 assigned to AsO3� 3 symmetric stretching vibration. Raman spectroscopy identifies three bands at 803, 758 and 661 cm�1 assigned to the symmetric and antisymmetric stretching vibrations of AsO3� 3 and As-OH stretching vibration respectively. In addition, the infrared bands observed at 1116, 1040, 1090, 981 and 616 cm�1, are assigned to the m3, m1 and m4 modes of SO2� 4 . The same bands are observed at 1287, 1085, 983 and 604 cm�1 in the Raman spectrum. As3d band at binding energy of 44.05 eV in XPS confirms arsenic valence of tooeleite is +3. These characteristic bands in the IR and Raman spectra provide useful basis for identifying the mineral tooeleite.

The molecular structure of matioliite – NaMgAl5(PO4)4(OH)6·2(H2O) : a pegmatite mineral from Minas Gerais, Brazil

Detailed spectroscopic and chemical investigation of matioliite, including infrared and Raman spectroscopy, scanning electron microscopy and electron probe microanalysis has been carried out on homogeneous samples from the Gentil pegmatite, Mendes Pimentel, Minas Gerais, Brazil. The chemical composition is (wt.%): FeO 2.20, CaO 0.05, Na2O 1.28, MnO 0.06, Al2O3 39.82, P2O5 42.7, MgO 4.68, F 0.02 and H2O 9.19; total 100.00. The mineral crystallize in the monoclinic crystal system, C2/c space group, with a = 25.075(1) Å, b = 5.0470(3) Å, c = 13.4370(7) Å, β = 110.97(3)°, V = 1587.9(4) Å3, Z = 4. Raman spectroscopy coupled with infrared spectroscopy supports the concept of phosphate, hydrogen phosphate and dihydrogen phosphate units in the structure of matioliite. Infrared and Raman bands attributed to water and hydroxyl stretching modes are identified. Vibrational spectroscopy adds useful information to the molecular structure of matioliite.

A vibrational spectroscopic study of the so-called ‘healing’ mineral papagoite CaCuAlSi2O6(OH)3

Papagoite is a silicate mineral named after an American Indian tribe and was used as a healing mineral. Papagoite CaCuAlSi2O6(OH)3 is a hydroxy mixed anion compound with both silicate and hydroxyl anions in the formula. The structural characterization of the mineral papagoite remains incomplete. Papagoite is a four-membered ring silicate with Cu2+ in square planar coordination. The intense sharp Raman band at 1053 cm−1 is assigned to the ν1 (A 1g) symmetric stretching vibration of the SiO4 units. The splitting of the ν3 vibrational mode offers support to the concept that the SiO4 tetrahedron in papagoite is strongly distorted. A very intense Raman band observed at 630 cm−1 with a shoulder at 644 cm−1 is assigned to the ν4 vibrational modes. Intense Raman bands at 419 and 460 cm−1 are attributed to the ν2 bending modes. Intense Raman bands at 3545 and 3573 cm−1 are assigned to the stretching vibrations of the OH units. Low-intensity Raman bands at 3368 and 3453 cm−1 are assigned to water stretching modes. It is suggested that the formula of papagoite is more likely to be CaCuAlSi2O6(OH)3 · xH2O. Hence, vibrational spectroscopy has been used to characterize the molecular structure of papagoite.

Vibrational spectroscopic characterization of the phosphate mineral anapaite Ca2Fe2+(PO4)2 · 4(H2O)

We have characterized anapaite Ca2Fe2+(PO4)2·4(H2O), a rare Ca and Fe phosphate, using a combination of electron microscopy and vibrational spectroscopy. The mineral occurs in soils and lacustrine sediments and is usually related to the diagenetic process in phosphorous rich sediments. The phosphate anion is characterized by its Raman spectrum with an intense sharp band at 943 cm-1, attributed to the ν1 PO4 3- symmetric stretching mode. Three bands at 992, 1039 and 1071 cm-1 are attributed to ν3 PO4 3-antisymmetric stretching modes. The infrared spectrum of anapaite shows complexity with a series of overlapping bands. Water in the structure of anapaite is observed by OH stretching vibrations at 2777, 3022 and 3176 cm-1 (Raman) and 2744, 3014 and 3096 cm-1 (infrared). The position of these bands provides evidence for the strong hydrogen bonding of water in the anapaite structure and contributes to the stability of the mineral.

Vibrational spectroscopic characterization of the phosphate mineral phosphophyllite – Zn2Fe(PO4)2·4H2O, from Hagendorf Süd, Germany and in comparison with other zinc phosphates

This research was undertaken on phosphophyllite sample from the Hagendorf Süd pegmatite, Bavaria, Germany. Chemical analysis was carried out by Scanning Electron Microscope in the EDS mode and indicates a zinc and iron phosphate with partial substitution of manganese, which partially replaced iron. The calculated chemical formula of the studied sample was determined to be: Zn2(Fe0.65, Mn0.35)P1.00(PO4)2- �4(H2O). The intense Raman peak at 995 cm�1 is assigned to the m1 PO3� 4 symmetric stretching mode and the two Raman bands at 1073 and 1135 cm�1 to the m3 PO3� 4 antisymmetric stretching modes. The m4 PO3� 4 bending modes are observed at 505, 571, 592 and 653 cm�1 and the m2 PO3� 4 bending mode at 415 cm�1. The sharp Raman band at 3567 cm�1 attributed to the stretching vibration of OH units brings into question the actual formula of phosphophyllite. Vibrational spectroscopy enables an assessment of the molecular structure of phosphophyllite to be assessed.

A Raman spectroscopic study of the basic carbonate mineral callaghanite Cu2Mg2(CO3)(OH)6⋅2H2O

Raman spectrum of callaghanite, Cu2Mg2(CO3)(OH)6⋅2H2O, was studied and compared with published Raman spectra of azurite, malachite and hydromagnesite. Stretching and bending vibrations of carbonate and hydroxyl units and water molecules were tentatively assigned. Approximate O–H…O hydrogen bond lengths were inferred from the spectra. Because of the high content of hydroxyl ions in the crystal structure in comparison with low content of carbonate units, callaghanite should be better classified as a carbonatohydroxide than a hydroxycarbonate.

The phosphate mineral arrojadite-(KFe) and its spectroscopic characterization

The arrojadite-(KFe) mineral has been analyzed using a combination of scanning electron microscopy and a combination of Raman and infrared spectroscopy. The origin of the mineral is Rapid Creek sedimentary phosphatic iron formation, northern Yukon. The formula of the mineral was determined as K2.06Na2Ca0.89Na3.23(Fe7.82Mg4.40Mn0.78)Σ13.00Al1.44(PO4)10.85(PO3OH0.23)(OH)2. The complexity of the mineral formula is reflected in the spectroscopy. Raman bands at 975, 991 and 1005 cm−1 with shoulder bands at 951 and 1024 cm−1 are assigned to the View the MathML source ν1 symmetric stretching modes. The Raman bands at 1024, 1066, 1092, 1123, 1148 and 1187 cm−1 are assigned to the View the MathML source ν3 antisymmetric stretching modes. A series of Raman bands observed at 540, 548, 557, 583, 604, 615 and 638 cm−1 are attributed to the ν4 out of plane bending modes of the PO4 and H2PO4 units. The ν2 PO4 and H2PO4 bending modes are observed at 403, 424, 449, 463, 479 and 513 cm−1. Hydroxyl and water stretching bands are readily observed. Vibrational spectroscopy enables new information about the complex phosphate mineral arrojadite-(KFe) to be obtained.

Vibrational spectroscopic characterization of the phosphate mineral hureaulite – (Mn, Fe)5(PO4)2(HPO4)2·4(H2O)

This research was done on hureaulite samples from the Cigana claim, a lithium bearing pegmatite with triphylite and spodumene. The mine is located in Conselheiro Pena, east of Minas Gerais. Chemical analysis was carried out by Electron Microprobe analysis and indicated a manganese rich phase with partial substitution of iron. The calculated chemical formula of the studied sample is: (Mn3.23, Fe1.04, Ca0.19, Mg0.13)(PO4)2.7(HPO4)2.6(OH)4.78. The Raman spectrum of hureaulite is dominated by an intense sharp band at 959 cm−1 assigned to PO stretching vibrations of HPO42− units. The Raman band at 989 cm−1 is assigned to the PO43− stretching vibration. Raman bands at 1007, 1024, 1047, and 1083 cm−1 are attributed to both the HOP and PO antisymmetric stretching vibrations of HPO42− and PO43− units. A set of Raman bands at 531, 543, 564 and 582 cm−1 are assigned to the ν4 bending modes of the HPO42− and PO43− units. Raman bands observed at 414, and 455 cm−1 are attributed to the ν2 HPO42− and PO43− units. The intense A series of Raman and infrared bands in the OH stretching region are assigned to water stretching vibrations. Based upon the position of these bands hydrogen bond distances are calculated. Hydrogen bond distances are short indicating very strong hydrogen bonding in the hureaulite structure. A combination of Raman and infrared spectroscopy enabled aspects of the molecular structure of the mineral hureaulite to be understood.

A vibrational spectroscopic study of the phosphate mineral cyrilovite Na(Fe3+)3(PO4)2(OH)4·2(H2O) and in comparison with wardite

Vibrational spectroscopy enables subtle details of the molecular structure of cyrilovite to be determined. Single crystals of a pure phase from a Brazilian pegmatite were used. Cyrilovite is the Fe3+ member of the wardite group. The infrared and Raman spectroscopy were applied to compare the structure of cyrilovite with that of wardite. The Raman spectrum of cyrilovite in the 800–1400 cm−1 spectral range shows two intense bands at 992 and 1055 cm−1 assigned to the ν1View the MathML source symmetric stretching vibrations. A series of low intensity bands at 1105, 1136, 1177 and 1184 cm−1 are assigned to the ν3View the MathML source antisymmetric stretching modes. The infrared spectrum of cyrilovite in the 500–1300 cm−1 shows much greater complexity than the Raman spectrum. Strong infrared bands are found at 970 and 1007 cm−1 and are attributed to the ν1View the MathML source symmetric stretching mode. Raman bands are observed at 612 and 631 cm−1 and are assigned to the ν4 out of plane bending modes of the View the MathML source unit. In the 2600–3800 cm−1 spectral range, intense Raman bands for cyrilovite are found at 3328 and 3452 cm−1 with a broad shoulder at 3194 cm−1 and are assigned to OH stretching vibrations. Sharp infrared bands are observed at 3485 and 3538 cm−1. Raman spectroscopy complimented with infrared spectroscopy has enabled the structure of cyrilovite to be ascertained and compared with that of wardite.

SEM-EDX, Raman and infrared spectroscopic characterization of the phosphate mineral frondelite (Mn2+)(Fe3+)4(PO4)3(OH)5

We have analyzed a frondelite mineral sample from the Cigana mine, located in the municipality of Conselheiro Pena, a well-known pegmatite in Brazil. In the Cigana pegmatite, secondary phosphates, namely eosphorite, fairfieldite, fluorapatite, frondelite, gormanite, hureaulite, lithiophilite, reddingite and vivianite are common minerals in miarolitic cavities and in massive blocks after triphylite. The chemical formula was determined as (Mn0.68, Fe0.32)(Fe3+)3,72(PO4)3.17(OH)4.99. The structure of the mineral was assessed using vibrational spectroscopy. Bands attributed to the stretching and bending modes of PO4 3- and HOPO3 3- units were identified. The observation of multiple bands supports the concept of symmetry reduction of the phosphate anion in the frondelite structure. Sharp Raman and infrared bands at 3581 cm−1 is assigned to the OH stretching vibration. Broad Raman bands at 3063, 3529 and 3365 cm−1 are attributed to water stretching vibrational modes.

Infrared and Raman spectroscopic characterization of the carbonate mineral weloganite – Sr3Na2Zr(CO3)6·3H2O and in comparison with selected carbonates

The mineral weloganite Na2Sr3Zr(CO3)6·3H2O has been studied by using vibrational spectroscopy and a comparison is made with the spectra of weloganite with other carbonate minerals. Weloganite is member of the mckelveyite group that includes donnayite-(Y) and mckelveyite-(Y). The Raman spectrum of weloganite is characterized by an intense band at 1082 cm−1 with shoulder bands at 1061 and 1073 cm−1, attributed to the View the MathML source symmetric stretching vibration. The observation of three symmetric stretching vibrations is very unusual. The position of View the MathML source symmetric stretching vibration varies with mineral composition. The Raman bands at 1350, 1371, 1385, 1417, 1526, 1546, and 1563 cm−1 are assigned to the ν3 (CO3)2− antisymmetric stretching mode. The observation of additional Raman bands for the ν3 modes for weloganite is significant in that it shows distortion of the carbonate anion in the mineral structure. The Raman band observed at 870 cm−1 is assigned to the (CO3)2− ν2 bending mode. Raman bands observed for weloganite at 679, 682, 696, 728, 736, 749, and 762 cm−1 are assigned to the (CO3)2− ν4 bending modes. A comparison of the vibrational spectra is made with that of the rare earth carbonates decrespignyite, bastnasite, hydroxybastnasite, parisite, and northupite.

Infrared and Raman spectroscopic characterisation of the sulphate mineral creedite – Ca3Al2SO4(F,OH)·2H2O – and in comparison with the alums

The mineral creedite is a fluorinated hydroxy hydrated sulphate of aluminium and calcium of formula Ca3Al2SO4(F,OH)·2H2O. The mineral has been studied by a combination of electron probe analysis to determine the molecular formula of the mineral and the structure assessed by vibrational spectroscopy. The spectroscopy of creedite may be compared with that of the alums. The Raman spectrum of creedite is characterised by an intense sharp band at 986 cm−1 assigned to the View the MathML source ν1 (Ag) symmetric stretching mode. Multiple bands of creedite in the antisymmetric stretching region support the concept of a reduction in symmetry of the sulphate anion. Multiple bands are also observed in the bending region with the three bands at 601, 629 and 663 cm−1 assigned to the View the MathML source ν4 (Ag) bending modes. The observation of multiple bands at 440, 457 and 483 cm−1 attributed to the View the MathML source ν2 (Bg) bending modes supports the concept that the symmetry of the sulphate is reduced by coordination to the water bonded to the Al3+ in the creedite structure. The splitting of the ν2, ν3 and ν4 modes is attributed to the reduction of symmetry of the SO4 and it is proposed that the sulphate coordinates to water in the hydrated aluminium in bidentate chelation.