DEGEO - Departamento de Geologia
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Resultados da Pesquisa
Item Assessment of the molecular structure of an intermediate member of the triplite-zwieselite mineral series : a raman and infrared study.(2014) Frost, Ray Leslie; Xi, Yunfei; López, Andrés; Moreira, Viviane Amaral; Cipriano, Ricardo Augusto Scholz; Lima, Rosa Malena Fernandes; Gandini, Antônio LucianoThe mineral series triplite-zwieselite with theoretical formula (Mn2þ)2(PO4)(F)-(Fe2þ)2(PO4)(F) from the El Criolo granitic pegmatite, located in the Eastern Pampean Ranges of Cordoba Province, was studied using electron microprobe, thermogravimetry, and Raman and infrared spec- troscopy. The analysis of the mineral provided a formula of (Fe1.00, Mn0.85, Ca0.08, Mg0.06)P2.00(PO4)1.00(F0.80, OH0.20)P1.00. An intense Raman band at 981cm1 with a shoulder at 977cm1 is assigned to the PO3 4 n1 symmetric stretching mode. The observation of two bands for the phosphate symmetric stretching mode offers support for the concept that the phosphate units in the structure of triplite-zwieselite are not equivalent. Low-intensity Raman bands at 1012, 1036, 1071, 1087, and 1127 cm1 are assigned to the PO3 4 n3 antisymmetric stretching modes. A set of Raman bands at 572, 604, 639, and 684 cm1 are attributed to the PO3 4 n4 out-of-plane bending modes. A single intense Raman band is found at 3508 cm1 and is assigned to the stretching vibration of hydroxyl units. Infrared bands are observed at 3018, 3125, and 3358 cm1 and are attributed to water stretching vibrations. Supplemental materials are available for this article. Go to the publisher’s online edition of Spectroscopy Letters to view the supplemental file.Item A Raman and infrared spectroscopic study of the phosphate mineral laueite.(2016) Frost, Ray Leslie; Cipriano, Ricardo Augusto Scholz; López, AndrésA laueite mineral sample from Lavra Da Ilha, Minas Gerais, Brazil has been studied by vibrational spectroscopy and scanning electron microscopy with EDX. Chemical formula calculated on the basis of semi-quantitative chemical analysis can be expressed as (Mn2+0.85,Fe2+0.10Mg0.05)P1.00(Fe3+1.90,Al0.10)P2.00(PO4)2(OH)2_8H2O. The laueite structure is based on an infinite chains of vertex-linked oxygen octahedra, with Fe3+ occupying the octahedral centers, the chain oriented parallel to the c-axis and linked by PO4 groups. Consequentially not all phosphate units are identical. Two intense Raman bands observed at 980 and 1045 cm_1 are assigned to the n1 PO43_ symmetric stretching mode. Intense Raman bands are observed at 525 and 551 cm_1 with a shoulder at 542 cm_1 are assigned to the n4 out of plane bending modes of the PO43_. The observation of multiple bands supports the concept of non-equivalent phosphate units in the structure. Intense Raman bands are observed at 3379 and 3478 cm_1 and are attributed to the OH stretching vibrations of the hydroxyl units. Intense broad infrared bands are observed. Vibrational spectroscopy enables subtle details of the molecular structure of laueite to be determined.Item SEM, EDX and vibrational spectroscopic study of the phosphate mineral ushkovite MgFe2 3+(PO4)2(OH)2 8H2O – implications of the molecular structure.(2015) López, Andrés; Cipriano, Ricardo Augusto Scholz; Frost, Ray Leslie; Belotti, Fernanda MariaThe mineral ushkovite has been analyzed using a combination of electron microscopy with EDX and vibrational spectroscopy. Chemical analysis shows the mineral contains P, Mg with very minor Fe. Thus, the formula of the studied ushkovite is Mg3 2+(PO4)2 8H2O. The Raman spectrum shows an intense band at 953 cm 1 assigned to the m1 symmetric stretching mode. In the infrared spectra complexity exists with multiple antisymmetric stretching vibrations observed, due to the reduced tetrahedral symmetry. This loss of degeneracy is also reflected in the bending modes. Strong infrared bands around 827 cm 1 are attributed to water librational modes. The Raman spectra of the hydroxyl-stretching region are complex with overlapping broad bands. Hydroxyl stretching vibrations are identified at 2881, 2998, 3107, 3203, 3284 and 3457 cm 1. The wavenumber band at 3457 cm 1 is attributed to the presence of FeOH groups. This complexity is reflected in the water HOH bending modes where a strong infrared band centered around 1653 cm 1 is found. Such a band reflects the strong hydrogen bonding of the water molecules to the phosphate anions in adjacent layers. Spectra show three distinct OH bending bands from strongly hydrogen-bonded, weakly hydrogen bonded water and non-hydrogen bonded water. Vibrational spectroscopy enhances our knowledge of the molecular structure of ushkovite.Item A vibrational spectroscopic study of the phosphate mineral vantasselite Al4(PO4)3(OH)3 9H2O.(2015) Frost, Ray Leslie; Cipriano, Ricardo Augusto Scholz; Belotti, Fernanda Maria; López, Andrés; Theiss, Frederick L.We have studied the phosphate mineral vantasselite Al4(PO4)3(OH)3 9H2O using a combination of SEM with EDX and Raman and infrared spectroscopy. Qualitative chemical analysis shows Al, Fe and P. Raman bands at 1013 and 1027 cm 1 are assigned to the PO43 m1 symmetric stretching mode. The observation of two bands suggests the non-equivalence of the phosphate units in the vantasselite structure. Raman bands at 1051, 1076 and 1090 cm 1 are attributed to the PO43 m3 antisymmetric stretching vibration. A comparison is made with the spectroscopy of wardite. Strong infrared bands at 1044, 1078, 1092, 1112, 1133, 1180 and 1210 cm 1 are attributed to the PO4 3 m3 antisymmetric stretching mode. Some of these bands may be due to dAl2OH deformation modes. Vibrational spectroscopy offers a mechanism for the study of the molecular structure of vantasselite.Item Raman and infrared spectroscopic study of turquoise minerals.(2015) Čejka, Jiři; Sejkora, Jiři; Macek, Ivo; Malíková, Radana; Wang, Lina; Cipriano, Ricardo Augusto Scholz; Xi, Yunfei; Frost, Ray LeslieRaman and infrared spectra of three well-defined turquoise samples, CuAl6(PO4)4(OH)8_4H2O, from Lavender Pit, Bisbee, Cochise county, Arizona; Kouroudaiko mine, Faleme river, Senegal and Lynch Station, Virginia were studied, interpreted and compared. Observed Raman and infrared bands were assigned to the stretching and bending vibrations of phosphate tetrahedra, water molecules and hydroxyl ions. Approximate O–H…O hydrogen bond lengths were inferred from the Raman and infrared spectra. No Raman and infrared bands attributable to the stretching and bending vibrations of (PO3OH)2_ units were observed.Item A vibrational spectroscopic study of the anhydrous phosphate mineral sidorenkite Na3Mn(PO4)(CO3).(2015) Frost, Ray Leslie; López, Andrés; Cipriano, Ricardo Augusto Scholz; Belotti, Fernanda Maria; Xi, YunfeiSidorenkite is a very rare low-temperature hydrothermal mineral, formed very late in the crystallization of hyperagpaitic pegmatites in a differentiated alkalic massif (Mt. Alluaiv, Kola Peninsula, Russia). Sidorenkite Na3Mn(PO4)(CO3) is a phosphate–carbonate of sodium and manganese. Such a formula with two oxyanions lends itself to vibrational spectroscopy. The sharp Raman band at 959 cm 1 and 1012 cm 1 are assigned to the PO43 stretching modes, whilst the Raman bands at 1044 cm 1 and 1074 cm 1 are attributed to the CO32 stretching modes. It is noted that no Raman bands at around 800 cm 1 for sidorenkite were observed. The infrared spectrum of sidorenkite shows a quite intense band at 868 cm 1 with other resolved component bands at 850 and 862 cm 1. These bands are ascribed to the CO32 out-of-plane bend (m2) bending mode. The series of Raman bands at 622, 635, 645 and 704 cm 1 are assigned to the m4 phosphate bending modes. The observation of multiple bands supports the concept of a reduction in symmetry of the carbonate anion from D3h or even C2v.Item Vibrational spectroscopic characterization of the phosphate mineral althausite Mg2(PO4)(OH,F,O) - implications for the molecular structure.(2014) Frost, Ray Leslie; López, Andrés; Xi, Yunfei; Cipriano, Ricardo Augusto ScholzNatural 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 m1 symmetric stretching modes 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 m4 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 m2 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.Item Raman, infrared and near-infrared spectroscopic characterization of the herderite-hydroxylherderite mineral series.(2014) Frost, Ray Leslie; Cipriano, Ricardo Augusto Scholz; López, Andrés; Xi, Yunfei; Queiroz, Camila de Siqueira; Belotti, Fernanda Maria; Cândido Filho, MauroNatural single-crystal specimens of the herderite–hydroxylherderite series from Brazil, with general formula CaBePO4(F,OH), were investigated by electron microprobe, Raman, infrared and near-infrared spectroscopies. The minerals occur as secondary products in granitic pegmatites. Herderite and hydroxylherderite minerals show extensive solid solution formation. The Raman spectra of hydroxylherderite are characterized by bands at around 985 and 998 cm_1, assigned to m1 symmetric stretching mode of the HOPO3_ 3 and PO3_ 4 units. Raman bands at around 1085, 1128 and 1138 cm_1 are attributed to both the HOP and PO antisymmetric stretching vibrations. The set of Raman bands observed at 563, 568, 577, 598, 616 and 633 cm_1 are assigned to the m4 out of plane bending modes of the PO4 and H2PO4 units. The OH Raman stretching vibrations of hydroxylherderite were observed ranging from 3626 cm_1 to 3609 cm_1. The infrared stretching vibrations of hydroxylherderites were observed between 3606 cm_1 and 3599 cm_1. By using a Libowitzky type function, hydrogen bond distances based upon the OH stretching bands were calculated. Characteristic NIR bands at around 6961 and 7054 cm_1 were assigned to the first overtone of the fundamental, whilst NIR bands at 10,194 and 10,329 cm_1 are assigned to the second overtone of the fundamental OH stretching vibration. Insight into the structure of the herderite–hydroxylherderite series is assessed by vibrational spectroscopy.Item A vibrational spectroscopic study of the phosphate mineral minyulite KAl2(OH,F)(PO4)2 4(H2O) and in comparison with wardite.(2014) Frost, Ray Leslie; López, Andrés; Xi, Yunfei; Cardoso, Luiz Henrique; Cipriano, Ricardo Augusto ScholzVibrational spectroscopy enables subtle details of the molecular structure of minyulite KAl2(OH,F)(PO4)2_ 4(H2O). Single crystals of a pure phase from a Brazilian pegmatite were used. Minyulite belongs to the orthorhombic crystal system. This indicates that it has three axes of unequal length, yet all are perpendicular to each other. The infrared and Raman spectroscopy were applied to compare the structure of minyulite with wardite. The reason for the comparison is that both are Al containing phosphate minerals. The Raman spectrum of minyulite shows an intense band at 1012 cm_1 assigned to the m1 PO3_ 4 symmetric stretching vibrations. A series of low intensity Raman bands at 1047, 1077, 1091 and 1105 cm_1 are assigned to the m3 PO3_ 4 antisymmetric stretching modes. The Raman bands at 1136, 1155, 1176 and 1190 cm_1 are assigned to AlOH deformation modes. The infrared band at 1014 cm_1 is ascribed to the PO3_ 4 m1 symmetric stretching vibrational mode. The infrared bands at 1049, 1071, 1091 and 1123 cm_1 are attributed to the PO3_ 4 m3 antisymmetric stretching vibrations. The infrared bands at 1123, 1146 and 1157 cm_1 are attributed to AlOH deformation modes. Raman bands at 575, 592, 606 and 628 cm_1 are assigned to the m4 out of plane bending modes of the PO3_ 4 unit. In the 2600– 3800 cm_1 spectral range, Raman bands for minyulite are found at 3661, 3669 and 3692 cm_1 are assigned to AlOH/AlF stretching vibrations. Broad infrared bands are also found at 2904, 3105, 3307, 3453 and 3523 cm_1. Raman bands at 3225, 3324 cm_1 are assigned to water stretching vibrations. A comparison is made with the vibrational spectra of wardite. Raman spectroscopy complimented with infrared spectroscopy has enabled aspects of the structure of minyulite to be ascertained and compared with that of other phosphate minerals.Item Vibrational spectroscopy of the phosphate mineral kovdorskite - Mg2PO4(OH)-3H2O.(2013) Frost, Ray Leslie; López, Andrés; Xi, Yunfei; Granja, Amanda; Cipriano, Ricardo Augusto Scholz; Lima, Rosa Malena FernandesThe mineral kovdorskite Mg2PO4(OH)_3H2O was studied by electron microscopy, thermal analysis and vibrational spectroscopy. A comparison of the vibrational spectroscopy of kovdorskite is made with other magnesium bearing phosphate minerals and compounds. Electron probe analysis proves the mineral is very pure. The Raman spectrum is characterized by a band at 965 cm_1 attributed to the PO3_ 4 m1 symmetric stretching mode. Raman bands at 1057 and 1089 cm_1 are attributed to the PO3_ 4 m3 antisymmetric stretching modes. Raman bands at 412, 454 and 485 cm_1 are assigned to the PO3_ 4 m2 bending modes. Raman bands at 536, 546 and 574 cm_1 are assigned to the PO3_ 4 m4 bending modes. The Raman spectrum in the OH stretching region is dominated by a very sharp intense band at 3681 cm_1 assigned to the stretching vibration of OH units. Infrared bands observed at 2762, 2977, 3204, 3275 and 3394 cm_1 are attributed to water stretching bands. Vibrational spectroscopy shows that no carbonate bands are observed in the spectra; thus confirming the formula of the mineral as Mg2PO4(OH)_3H2O.