Vibrational spectroscopy of the borate mineral pinnoite MgB2O(OH)6

There is a large number of boron containing minerals with water and/or hydroxyl units of which pinnoite MgB2O(OH)6 is one. Some discussion about the molecular structure of pinnoite exists in the literature. Whether water is involved in the structure is ill-determined. The molecular structure of pinnoite has been assessed by the combination of Raman and infrared spectroscopy. The Raman spectrum is characterized by an intense band at 900 cm−1 assigned to the BO stretching vibrational mode. A series of bands in the 1000–1320 cm−1 spectral range are attributed to BO antisymmetric stretching modes and in-plane bending modes. The infrared spectrum shows complexity in this spectral range. Multiple Raman OH stretching vibrations are found at 3179, 3399, 3554 and 3579 cm−1. The infrared spectrum shows a series of overlapping bands with bands identified at 3123, 3202, 3299, 3414, 3513 and 3594 cm−1. By using a Libowitzky type function, hydrogen bond distances were calculated. Two types of hydrogen bonds were identified based upon the hydrogen bond distance. It is important to understand the structure of pinnoite in order to form nanomaterials based upon the pinnoite structure.

A Raman spectroscopic comparison of calcite and dolomite

Raman spectroscopy was used to characterize and differentiate the two minerals calcite and dolomite and the bands related to the mineral structure. The (CO3)2− group is characterized by four prominent Raman vibrational modes: (a) the symmetric stretching, (b) the asymmetric deformation, (c) asymmetric stretching and (d) symmetric deformation. These vibrational modes of the calcite and dolomite were observed at 1440, 1088, 715 and 278 cm−1. The significant differences between the minerals calcite and dolomite are observed by Raman spectroscopy. Calcite shows the typical bands observed at 1361, 1047, 715 and 157 cm−1, and the special bands at 1393, 1098, 1069, 1019, 299, 258 and 176 cm−1 for dolomite are observed. The difference is explained on the basis of the structure variation of the two minerals. Calcite has a trigonal structure with two molecules per unit cell, and dolomite has a hexagonal structure. This is more likely to cause the splitting and distorting of the carbonate groups. Another cause for the difference is the cation substituting for Mg in the dolomite mineral.

Vibrational spectroscopy of the silicate mineral plumbotsumite Pb5(OH)10Si4O8 : an assessment of the molecular structure

We have used scanning electron microscopy with energy dispersive X-ray analysis to determine the precise formula of plumbotsumite, a rare lead silicate mineral of formula Pb5(OH)10Si4O8. This study forms the first systematic study of plumbotsumite from the Bigadic deposits, Turkey. Vibrational spectroscopy was used to assess the molecular structure of plumbotsumite as the structure is not known. The mineral is characterized by sharp Raman bands at 1047, 1055 and 1060 cm−1 assigned to SiO stretching vibrational modes and sharp Raman bands at 673, 683 and 697 cm−1 assigned to OSiO bending modes. The observation of multiple bands offers support for a layered structure with variable SiO3 structural units. Little information may be obtained from the infrared spectra because of broad spectral profiles. Intense Raman bands at 3510, 3546 and 3620 cm−1 are ascribed to OH stretching modes. Evidence for the presence of water in the plumbotsumite structure was inferred from the infrared spectra.

Vibrational spectroscopy of the borate mineral gaudefroyite Ca4Mn3+3-x(BO3)3(CO3)(O,OH) from N’Chwaning II mine, Kalahari, Republic of South Africa

Gaudefroyite Ca4Mn3+3-x(BO3)3(CO3)(O,OH)3 is an unusual mineral containing both borate and carbonate groups and is found in the oxidation zones of manganese minerals, and it is black in color. Vibrational spectroscopy has been used to explore the molecular structure of gaudefroyite. Gaudefroyite crystals are short dipyramidal or prismatic with prominent pyramidal terminations, to 5 cm. Two very sharp Raman bands at 927 and 1076 cm-1are assigned to trigonal borate and carbonate respectively. Broad Raman bands at 1194, 1219 and 1281 cm-1 are attributed to BOH in-plane bending modes. Raman bands at 649 and 670 cm-1 are assigned to the bending modes of trigonal and tetrahedral boron. Infrared spectroscopy supports these band assignments. Raman bands in the OH stretching region are of a low intensity. The combination of Raman and infrared spectroscopy enables the assessment of the molecular structure of gaudefroyite to be made.

Vibrational spectroscopy of the borate mineral chambersite MnB7O13Cl – Implications for the molecular structure

Chambersite is a manganese borate mineral with formula: MnB7O13Cl and occurs as colorless crystals in the monoclinic pyramidal crystal system. Raman bands at 902, 920, 942 and 963 cm-1 are assigned to the BO stretching vibration of the B7O13 units. Raman bands at 1027, 1045, 1056, 1075 and 1091 cm-1 are attributed to the BCl in-plane bending modes. The intense infrared band at 866 cm-1 is assigned to the trigonal borate stretching modes. The Raman band at 660 cm-1 together with bands at 597, 642 679, 705 and 721 cm-1 are assigned to the trigonal and tetrahedral borate bending modes. The molecular structure of a natural chambersite has been assessed using vibrational spectroscopy.

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.

Infrared and Raman spectroscopic characterization of the borate mineral hydroboracite CaMg[B3O4(OH)3]2⋅3H2O : implications for the molecular structure

We have studied the mineral hydroboracite CaMg[B3O4(OH)3]2∙3H2O using electron microscopy and vibrational spectroscopy. Both tetrahedral and trigonal boron units are observed. The nominal resolution of the Raman spectrometer is of the order of 2 cm-1 and as such is sufficient enough to identify separate bands for the stretching bands of the two boron isotopes. The Raman band at 1039 cm-1 is assigned to BO stretching vibration. Raman bands at 1144, 1157, 1229, 1318 cm-1 are attributed to the BOH in-plane bending modes. Raman bands at 825 and 925 cm-1 are attributed to the antisymmetric stretching modes of tetrahedral boron. The sharp Raman peak at 925 cm-1 is from the 11-B component such a mode, then it should have a smaller 10-B satellite near (1.03)x(925) = 952 cm-1, and indeed a small peak at 955 is observed. Four sharp Raman bands observed at 3371, 3507, 3563 and 3632 cm-1 are attributed to the stretching vibrations of hydroxyl units. The broad Raman bands at 3076, 3138, 3255, 3384 and 3551 cm-1 are assigned to water stretching vibrations. Infrared bands at 3367, 3505, 3559 and 3631 cm-1are assigned to the stretching vibration of the hydroxyl units. Broad infrared bands at 3072 and 3254 cm-1 are assigned to water stretching vibrations. Infrared bands at 1318, 1349, 1371, 1383 cm-1 are assigned to the antisymmetric stretching vibrations of trigonal boron

Vibrational spectroscopy of the borate mineral tunellite SrB6O9(OH)2·3(H2O) : implications for the molecular structure

Tunellite is a strontium borate mineral with formula: SrB6O9(OH)2∙3(H2O) and occurs as colorless crystals in the monoclinic pyramidal crystal system. An intense Raman band at 994 cm-1 was assigned to the BO stretching vibration of the B2O3 units. Raman bands at 1043, 1063, 1082 and 1113 cm-1 are attributed to the in-plane bending vibrations of trigonal boron. Sharp Raman bands observed at 464, 480, 523, 568 and 639 cm-1 are simply defined as trigonal and tetrahedral borate bending modes. The Raman spectrum clearly shows intense Raman bands at 3567 and 3614 cm-1, attributed to OH units. The molecular structure of a natural tunellite has been assessed by using vibrational spectroscopy.

Infrared and Raman spectroscopic characterization of the Borate mineral Vonsenite

There are a large number of boron-containing minerals, of which vonsenite is one. Some discussion about the molecular structure of vonsenite exists in the literature. Whether water is involved in the structure is ill-determined. The molecular structure of vonsenite has been assessed by the combination of Raman and infrared spectroscopy. The Raman spectrum is characterized by two intense broad bands at 997 and 1059 cm−1 assigned to the BO stretching vibrational mode. A series of Raman bands in the 1200–1500 cm−1 spectral range are attributed to BO antisymmetric stretching modes and in-plane bending modes. The infrared spectrum shows complexity in this spectral range. No Raman spectrum of water in the OH stretching region could be obtained. The infrared spectrum shows a series of overlapping bands with bands identified at 3037, 3245, 3443, 3556, and 3614 cm−1. It is important to understand the structure of vonsenite in order to form nanomaterials based on its structure. Vibrational spectroscopy enables a better understanding of the structure of vonsenite.

Vibrational spectroscopy of the copper (II) disodium sulphate dihydrate mineral kröhnkite Na2Cu(SO4)2 · 2H2O

A natural single-crystal specimen of the kröhnkite from Chuquicamata, Chile, with the general formula Na2Cu(SO4)2 · 2H2O, was investigated by Raman and infrared spectroscopy. The mineral kröhnkite is found in many parts of the world's arid areas. Kröhnkite crystallizes in the monoclinic crystal system with point group 2/m and space group P21/c. It is an uncommon secondary mineral formed in the oxidized zone of copper deposits, typically in very arid climates. The Raman spectrum of kröhnkite dominated by a very sharp intense band at 992 cm−1 is assigned to the ν1 symmetric stretching mode and Raman bands at 1046, 1049, 1138, 1164, and 1177 cm−1 are assigned to the ν3 antisymmetric stretching vibrations. The infrared spectrum shows an intense band at 992 cm−1. The Raman bands at 569, 582, 612, 634, 642, 655, and 660 cm−1 are assigned to the ν4 bending modes. Three Raman bands observed at 429, 445, and 463 cm−1 are attributed to the ν2 bending modes. The observation that three or four bands are seen in the ν4 region of kröhnkite is attributed to the reduction of symmetry to C2v or less.

Effect of Al content on the structure of Al-substituted goethite : a micro-Raman spectroscopic study

The characterization of X-ray diffraction, X-ray fluorescence, and field emission scanning electron microscope were used to confirm the successful preparation of Al-substituted goethite with different Al content. The micro-Raman spectroscopy was utilized to investigate the effect of Al content on the goethite lattice. The results show that all the feature bands of goethite shifted to high wavenumbers after the occurrence of Al substitution for Fe in the structure of goethite. The shift of wavenumber shows a good linear relationship as a function of increasing Al content especially for the band at 299 cm−1 (R2 = 0.9992). The in situ Raman spectroscopy of thermally treated goethite indicated that the Al substitution not only hinders the transformation of goethite, but also retarded the crystallization of thermally formed hematite. All the results indicated that Raman spectrum displayed an excellent performance in characterizing Al-substituted goethite, which implied the promising application in other substituted metal oxides or hydroxides.

Molecular structural studies of the amorphous mineral pitticite Fe, AsO4, SO4, H2O

Some minerals are colloidal and show no X-ray diffraction patterns. Vibrational spectroscopy offers one of the few methods for the assessment of the structure of these types of mineral. Among this group of minerals is pitticite simply described as Fe, AsO4, SO4, H2O. The objective of this research is to determine the molecular structure of the mineral pitticite using vibrational spectroscopy. Raman microscopy offers a useful method for the analysis of such colloidal minerals. Raman and infrared bands are attributed to the , and water stretching vibrations. The Raman spectrum is dominated by a very intense sharp band at 983 cm−1 assigned to the symmetric stretching mode. A strong Raman band at 1041 cm−1 is observed and is assigned to the antisymmetric stretching mode. Low intensity Raman bands at 757 and 808 cm−1 may be assigned to the antisymmetric and symmetric stretching modes. Raman bands observed at 432 and 465 cm−1 are attributable to the doubly degenerate ν2(SO4)2- bending mode.

The crystal structure and vibrational spectroscopy of jarosite and alunite minerals

The alunite supergroup of minerals is a large hydroxy-sulfate mineral group, which has seen renewed interest following their discovery on Mars. Numerous reviews exist concerning nomenclature, formation, and natural occurrence of this mineral group. Sulfate minerals in general are widely studied and their vibrational spectra are well characterized. However, no specific review concerning alunite and jarosite spectroscopy and crystal structure has been forthcoming. This review focuses on the controversial aspects of the crystal structure and vibrational spectroscopy of jarosite and alunite minerals. Inconsistencies regarding band assignments especially in the 1000–400 cm−1 region plague these two mineral groups and result in different band assignments among the various spectroscopic studies. There are significant crystallographic and magnetic structure ambiguities with regards to ammonium and hydronium end-members, namely, the geometry these two ions assume in the structure and the fact that hydronium jarosite is a spin glass. It was also found that the synthetic causes for the super cell in plumbojarosite, minamiite, huangite, and walthierite are not known.

Vibrational spectroscopy of the sulphate mineral sturmanite from Kuruman manganese deposits, South Africa

The mineral sturmanite is a hydrated calcium iron aluminium manganese sulphate tetrahydroxoborate hydroxide of formula Ca6(Fe, Al, Mn)2(SO4)2(B(OH)4)(OH)12•26H2O. We have studied the mineral sturmanite using a number of techniques, including SEM with EPMA and vibrational spectroscopy. Chemical analysis shows a homogeneous phase, composed by Ca, Fe, Mn, S, Al and Si. B is not determined in this EPMA technique. An intense Raman band at 990 cm−1 is assigned to the SO42− symmetric stretching mode. Raman spectroscopy identifies multiple sulphate symmetric stretching modes in line with the three sulphate crystallographically different sites. Raman spectroscopy also identifies a band at 1069 cm−1 which may be attributed to a carbonate symmetric stretching mode, indicating the presence of thaumasite. Infrared spectra display two bands at 1080 and 1107 cm−1 assigned to the SO42− antisymmetric stretching modes. The observation of multiple bands in this ν4 spectral region offers evidence for the reduction in symmetry of the sulphate anion from Td to C2v or even lower symmetry. The Raman band at 3622 cm−1 is assigned to the OH unit stretching vibration and the broad feature at around 3479 cm−1 to water stretching bands. Infrared spectroscopy shows a set of broad overlapping bands in the OH stretching region. Vibrational spectroscopy enables an assessment of the molecular structure of sturmanite to be made.

A vibrational spectroscopic study of the silicate mineral lomonosovite Na5Ti2(Si2O7)(PO4)O2

The mineral lomonosovite has been studied using a combination of scanning electron microscopy with energy dispersive X-ray analysis and vibrational spectroscopy. Qualitative chemical analysis gave Si, P, Na and Ti as the as major elements with small amounts of Mn, Ca, Fe and Al. The mineral lomonosovite has a formula Na5Ti2(Si2O7)(PO4)O2. Raman bands observed at 909, 925 and 939 cm−1 are associated with phosphate units. Raman bands found at 975, 999, 1070, 1080 and 1084 cm−1 are attributed to siloxane stretching vibrations. The observation of multiple bands in both the phosphate stretching and bending regions supports the concept that the symmetry of the phosphate anion in the structure of lomonosovite is significantly reduced. Infrared spectroscopy identifies bands in the water stretching and bending regions, thus suggesting that water is involved with the structure of lomonosovite either through adsorption on the surface or by bonding to the phosphate units.