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.

The molecular structure of the phosphate mineral chalcosiderite – a vibrational spectroscopic study

The mineral chalcosiderite with formula CuFe6(PO4)4(OH)8⋅4H2O has been studied by Raman spectroscopy and by infrared spectroscopy. A comparison of the chalcosiderite spectra is made with the spectra of turquoise. The spectra of the mineral samples are very similar in the 1200–900 cm−1 region but strong differences are observed in the 900–100 cm−1 region. The effect of substitution of Fe for Al in chalcosiderite shifts the bands to lower wave numbers. Factor group analysis (FGA) implies four OH stretching vibrations for both the water and hydroxyl units. Two bands ascribed to water are observed at 3276 and 3072 cm−1. Three hydroxyl stretching vibrations are observed. Calculations using a Libowitzky type formula show that the hydrogen bond distances of the water molecules are 2.745 and 2.812 Å which are considerably shorter than the values for the hydroxyl units 2.896, 2.917 and 2.978 Å. Two phosphate stretching vibrations at 1042 and 1062 cm−1 in line with the two independent phosphate units in the structure of chalcosiderite. Three bands are observed at 1102, 1159 and 1194 cm−1 assigned to the phosphate antisymmetric stretching vibrations. FGA predicts six bands but only three are observed due to accidental degeneracy. Both the ν2 and ν4 bending regions are complex. Four Raman bands observed at 536, 580, 598 and 636 cm−1 are assigned to the ν4 bending modes. Raman bands at 415, 420, 475 and 484 cm−1are assigned to the phosphate ν2 bending modes. Vibrational spectroscopy enables aspects of the molecular structure of chalcosiderite to be assessed.

The molecular structure of the phosphate mineral väyrynenite : a vibrational spectroscopic study

We have studied the mineral väyrynenite from the Viitaniemi pegmatite, located in the Eräjärvi area, Finland using a combination of electron microscopy electron microprobe and vibrational spectroscopic techniques. Chemical analysis shows the formula of the mineral to be (Mn0.88,Fe0.08,Mg0.01)∑0.97Be1.02(PO4)1.00(OH)1.02. Vibrational spectroscopy enables an assessment of the molecular structure of väyrynenite to be assessed. An intense Raman band at 1004 cm−1 is to the ν1 symmetric stretching mode. The observation of multiple bands in the phosphate stretching region, offers support for the concept of different phosphate units in the väyrynenite structure. Infrared spectroscopy confirms this multiplicity of vibrational bands. Multiple bands are observed in the phosphate bending region.

Characterization of the sulphate mineral amarantite Fe3 2 3+ (SO4)O 7H2O using infrared, Raman spectroscopy and thermogravimetry

The mineral amarantite Fe23+(SO4)O∙7H2O has been studied using a combination of techniques including thermogravimetry, electron probe analyses and vibrational spectroscopy. Thermal analysis shows decomposition steps at 77.63, 192.2, 550 and 641.4°C. The Raman spectrum of amarantite is dominated by an intense band at 1017 cm-1 assigned to the SO42- ν1 symmetric stretching mode. Raman bands at 1039, 1054, 1098, 1131, 1195 and 1233 cm-1 are attributed to the SO42- ν3 antisymmetric stretching modes. Very intense Raman band is observed at 409 cm-1 with shoulder bands at 399, 451 and 491 cm-1 are assigned to the v2 bending modes. A series of low intensity Raman bands are found at 543, 602, 622 and 650 cm-1 are assigned to the v4 bending modes. A very sharp Raman band at 3529 cm-1 is assigned to the stretching vibration of OH units. A series of Raman bands observed at 3025, 3089, 3227, 3340, 3401 and 3480 cm-1 are assigned to water bands. Vibrational spectroscopy enables aspects of the molecular structure of the mineral amarantite to be ascertained.

Vibrational spectroscopic characterization of the phosphate mineral series eosphorite–childrenite–(Mn,Fe)Al(PO4)(OH)2·(H2O)

The phosphate mineral series eosphorite–childrenite–(Mn,Fe)Al(PO4)(OH)2·(H2O) has been studied using a combination of electron probe analysis and vibrational spectroscopy. Eosphorite is the manganese rich mineral with lower iron content in comparison with the childrenite which has higher iron and lower manganese content. The determined formulae of the two studied minerals are: (Mn0.72,Fe0.13,Ca0.01)(Al)1.04(PO4, OHPO3)1.07(OH1.89,F0.02)·0.94(H2O) for SAA-090 and (Fe0.49,Mn0.35,Mg0.06,Ca0.04)(Al)1.03(PO4, OHPO3)1.05(OH)1.90·0.95(H2O) for SAA-072. Raman spectroscopy enabled the observation of bands at 970 cm−1 and 1011 cm−1 assigned to monohydrogen phosphate, phosphate and dihydrogen phosphate units. Differences are observed in the area of the peaks between the two eosphorite minerals. Raman bands at 562 cm−1, 595 cm−1, and 608 cm−1 are assigned to the �4 bending modes of the PO4, HPO4 and H2PO4 units; Raman bands at 405 cm−1, 427 cm−1 and 466 cm−1 are attributed to the �2 modes of these units. Raman bands of the hydroxyl and water stretching modes are observed. Vibrational spectroscopy enabled details of the molecular structure of the eosphorite mineral series to be determined.

The molecular structure of the phosphate mineral senegalite Al2(PO4)(OH)3⋅3H2O – A vibrational spectroscopic study

We have studied the mineral senagalite, a hydrated hydroxy phosphate of aluminium with formula Al2(PO4)(OH)3⋅3H2O using a combination of electron microscopy and vibrational spectroscopy. Senegalite crystal aggregates shows tabular to prismatic habitus and orthorhombic form. The Raman spectrum is dominated by an intense band at 1029 cm−1 assigned to the PO43- ν1 symmetric stretching mode. Intense Raman bands are found at 1071 and 1154 cm−1 with bands of lesser intensity at 1110, 1179 and 1206 cm−1 and are attributed to the PO43- ν3 antisymmetric stretching vibrations. The infrared spectrum shows complexity with a series overlapping bands. A comparison is made with spectra of other aluminium containing phosphate minerals such as augelite and turquoise. Multiple bands are observed for the phosphate bending modes giving support for the reduction of symmetry of the phosphate anion. Vibrational spectroscopy offers a means for the assessment of the structure of senagalite.

Vibrational spectroscopic characterization of the phosphate mineral kulanite Ba(Fe2+,Mn2+,Mg)2(Al,Fe3+)2(PO4)3(OH)3

The mineral kulanite BaFe2Al2(PO4)3(OH)3, a barium iron aluminum phosphate, has been studied by using a combination of electron microscopy and vibrational spectroscopy. Scanning electron microscopy with EDX shows the mineral is homogenous with no other phases present. The Raman spectrum is dominated by an intense band at 1022 cm−1 assigned to the PO43-ν1 symmetric stretching mode. Low intensity Raman bands at 1076, 1110, 1146, 1182 cm−1 are attributed to the PO43-ν3 antisymmetric stretching vibrations. The infrared spectrum shows a complex spectral profile with overlapping bands. Multiple phosphate bending vibrations supports the concept of a reduction in symmetry of the phosphate anion. Raman spectrum at 3211, 3513 and 3533 cm−1 are assigned to the stretching vibrations of the OH units. Vibrational spectroscopy enables aspects on the molecular structure of kulanite to be assessed.

Vibrational spectroscopic characterization of the phosphate mineral bermanite–Mn2+Mn23+(PO4)2(OH)2.4(H2O)

Bermanite Mn2þMn3þ2 ðPO4Þ2ðOHÞ2 � 4ðH2OÞ is a mixed valent hydrated hydroxy phosphate mineral. The mineral is reddish-brown and occurs in crystal aggregates and as lamellar masses. Bermanite is a common mineral in granitic pegmatites. The chemical composition of bermanite was obtained using EDS techniques. We have studied the molecular structure of bermanite using vibrational spectroscopy. The mineral is characterized by a Raman doublet at 991 and 999 cm-1 attributed to the phosphate stretching mode of two non-equivalent phosphate units. Raman bands at 1071, 1117 and 1142 cm-1 are assigned to the phosphate antisymmetric stretching modes. The hydroxyl stretching spectral region is complex with overlapping bands attributed to water and hydroxyl stretching vibrations. Vibrational spectroscopy proves most useful for the study of the mineral bermanite.

Thermal analysis and vibrational spectroscopic characterization of the boro silicate mineral datolite – CaBSiO4(OH)

The objective of this work is to determine the thermal stability and vibrational spectra of datolite CaBSiO4(OH) and relate these properties to the structure of the mineral. The thermal analysis of datolite shows a mass loss of 5.83% over a 700–775 °C temperature range. This mass loss corresponds to 1 water (H2O) molecules pfu. A quantitative chemical analysis using electron probe was undertaken. The Raman spectrum of datolite is characterized by bands at 917 and 1077 cm−1 assigned to the symmetric stretching modes of BO and SiO tetrahedra. A very intense Raman band is observed at 3498 cm−1 assigned to the stretching vibration of the OH units in the structure of datolite. BOH out-of-plane vibrations are characterized by the infrared band at 782 cm−1. The vibrational spectra are based upon the structure of datolite based on sheets of four- and eight-membered rings of alternating SiO4 and BO3(OH) tetrahedra with the sheets bonded together by calcium atoms.

Vibrational spectroscopic characterization of the sulphate mineral khademite Al(SO4)F⋅5(H2O)

Vibrational spectroscopy has been used to characterize the sulphate mineral khademite Al(SO4)F∙5(H2O). Raman band at 991 cm-1 with a shoulder at 975 cm-1 is assigned to the ν1 (SO4)2- symmetric stretching mode. The observation of two symmetric stretching modes suggests that the sulphate units are not equivalent. Two low intensity Raman bands at 1104 and 1132 cm-1 are assigned to the ν3 (SO4)2- antisymmetric stretching mode. The broad Raman band at 618 cm-1 is assigned to the v4 (SO4)2- bending modes. Raman bands at 455, 505 and 534 cm-1 are attributable to the doubly degenerate v2 (SO4)2- bending modes. Raman bands at 2991, 3146 and 3380 cm-1 are assigned to the OH stretching bands of water. Five infrared bands are noted at 2458, 2896, 3203, 3348 and 3489 cm-1 are also due to water stretching bands. The observation of multiple water stretching vibrations gives credence to the non-equivalence of water units in the khademite structure. Vibrational spectroscopy enables an assessment of the structure of khademite.

Vibrational spectroscopic characterization of the phosphate mineral barbosalite Fe2+Fe3+2(PO4)2(OH)2 : implications for the molecular structure

Natural single-crystal specimens of barbosalite from Brazil, with general formula Fe2+Fe3+ 2 (PO4)2(OH)2 were investigated by Raman and infrared spectroscopy. The mineral occurs as secondary products in granitic pegmatites. The Raman spectrum of barbosalite is characterized by bands at 1020, 1033 and 1044 cm−1 cm−1, assigned to ν1 symmetric stretching mode of the HOPO3- 3 and PO3- 4 units. Raman bands at around 1067, 1083 and 1138 cm−1 are attributed to both the HOP and PO antisymmetric stretching vibrations. The set of Raman bands observed at 575, 589 and 606 cm−1 are assigned to the ν4 out of plane bending modes of the PO4 and H2PO4 units. Raman bands at 439, 461, 475 and 503 cm−1 are attributed to the ν2 PO4 and H2PO4 bending modes. Strong Raman bands observed at 312, 346 cm−1 with shoulder bands at 361, 381 and 398 cm−1 are assigned to FeO stretching vibrations. No bands which are attributable to water vibrations were found. Vibrational spectroscopy enables aspects of the molecular structure of barbosalite to be assessed.

The molecular structure of the borate mineral inderite Mg(H4B3O7)(OH)⋅5H2O – A vibrational spectroscopic study

We have undertaken a study of the mineral inderite Mg(H4B3O7)(OH)⋅5H2O a hydrated hydroxy borate mineral of magnesium using scanning electron microscopy, thermogravimetry and vibrational spectroscopic techniques. The structure consists of [B3O3(OH)5]2-[B3O3(OH)5]2- soroborate groups and Mg(OH)2(H2O)4 octahedra interconnected into discrete molecules by the sharing of two OH groups. Thermogravimetry shows a mass loss of 47.2% at 137.5 °C, proving the mineral is thermally unstable. Raman bands at 954, 1047 and 1116 cm−1 are assigned to the trigonal symmetric stretching mode. The two bands at 880 and 916 cm−1 are attributed to the symmetric stretching mode of the tetrahedral boron. Both the Raman and infrared spectra of inderite show complexity. Raman bands are observed at 3052, 3233, 3330, 3392 attributed to water stretching vibrations and 3459 cm−1 with sharper bands at 3459, 3530 and 3562 cm−1 assigned to OH stretching vibrations. Vibrational spectroscopy is used to assess the molecular structure of inderite.

Vibrational spectroscopic characterization of the phosphate mineral althausite Mg2(PO4)(OH,F,O) – implications for the molecular structure

Natural single-crystal specimens of althausite from Brazil, with general formula Mg2(PO4)(OH,F,O) were investigated by Raman and infrared spectroscopy. The mineral occurs as a secondary product in granitic pegmatites. The Raman spectrum of althausite is characterized by bands at 1020, 1033 and 1044 cm-1, assigned to ν1 symmetric stretching modes of the HOPO33- and PO43- units. Raman bands at around 1067, 1083 and 1138 cm-1 are attributed to both the HOP and PO antisymmetric stretching vibrations. The set of Raman bands observed at 575, 589 and 606 cm-1 are assigned to the ν4 out of plane bending modes of the PO4 and H2PO4 units. Raman bands at 439, 461, 475 and 503 cm-1 are attributed to the ν2 PO4 and H2PO4 bending modes. Strong Raman bands observed at 312, 346 cm-1 with shoulder bands at 361, 381 and 398 cm-1 are assigned to MgO stretching vibrations. No bands which are attributable to water were found. Vibrational spectroscopy enables aspects of the molecular structure of althausite to be assessed.

A vibrational spectroscopic study of the silicate mineral ardennite-(As)

We have used a combination of scanning electron microscopy with EDX and vibrational spectroscopy to study the mineral ardennite-(As). The mineral ardennite-(As) of accepted formula Mn2þ 4 (Al,Mg)6(Si3O10)(SiO4)2(AsO4,VO4)(OH)6 is a silicate mineral which may contain arsenate and/or vanadates anions. Because of the oxyanions present, the mineral lends itself to analysis by Raman and infrared spectroscopy. Qualitative chemical analysis shows a homogeneous phase, composed by Si, Mn, Al and As. Ca and V were also observed in partial substitution for Mn and As. Raman bands at 1197, 1225, 1287 and 1394 cm-1 are assigned to SiO stretching vibrations. The strong Raman bands at 779 and 877 cm-1 are assigned to the AsO3- 4 antisymmetric and symmetric stretching vibrations. The Raman band at 352 cm-1 is assigned to the m2 symmetric bending vibration. The series of Raman bands between 414 and 471 cm-1 are assigned to the m4 out of plane bending modes of the AsO3-4 units. Intense Raman bands observed at 301 and 314 cm-1 are attributed to the MnO stretching and bending vibrations. Raman bands at 3041, 3149, 3211 and 3298 cm-1 are attributed to the stretching vibrations of OH units. There is vibrational spectroscopic evidence for the presence of water adsorbed on the ardennite-(As) surfaces.

A study of the phosphate mineral kapundaite NaCa(Fe3+)4(PO4)4(OH)3⋅5(H2O) using SEM/EDX and vibrational spectroscopic methods

Vibrational spectroscopy enables subtle details of the molecular structure of kapundaite to be determined. Single crystals of a pure phase from a Brazilian pegmatite were used. Kapundaite is the Fe3+ member of the wardite group. The infrared and Raman spectroscopy were applied to compare the structure of kapundaite with wardite. The Raman spectrum of kapundaite in the 800–1400 cm−1 spectral range shows two intense bands at 1089 and 1114 cm−1 assigned to the ν1PO43- symmetric stretching vibrations. The observation of two bands provides evidence for the non-equivalence of the phosphate units in the kapundaite structure. The infrared spectrum of kapundaite in the 500–1300 cm−1 shows much greater complexity than the Raman spectrum. Strong infrared bands are found at 966, 1003 and 1036 cm−1 and are attributed to the ν1PO43- symmetric stretching mode and ν3PO43- antisymmetric stretching mode. Raman bands in the ν4 out of plane bending modes of the PO43- unit support the concept of non-equivalent phosphate units in the kapundaite structure. In the 2600–3800 cm−1 spectral range, Raman bands for kapundaite are found at 2905, 3151, 3311, 3449 and 3530 cm−1. These bands are broad and are assigned to OH stretching vibrations. Broad infrared bands are also found at 2904, 3105, 3307, 3453 and 3523 cm−1 and are attributed to water. Raman spectroscopy complimented with infrared spectroscopy has enabled aspects of the structure of kapundaite to be ascertained and compared with that of other phosphate minerals.