Vibrational spectroscopic characterization of the phosphate mineral ludlamite (Fe,Mn,Mg)3(PO4)2⋅4H2O – a mineral found in lithium bearing pegmatites

The objective of this work is to analyze ludlamite (Fe,Mn,Mg)3(PO4)2⋅4H2O from Boa Vista mine, Galiléia, Brazil and to assess the molecular structure of the mineral. The phosphate mineral ludlamite has been characterized by EMP-WDS, Raman and infrared spectroscopic measurements. The mineral is shown to be a ferrous phosphate with some minor substitution of Mg and Mn. Raman bands at 917 and 950 cm−1 are assigned to the symmetric stretching mode of and units. Raman bands at 548, 564, 599 and 634 cm−1 are assigned to the ν4 bending modes. Raman bands at 2605, 2730, 2896 and 3190 cm−1 and infrared bands at 2623, 2838, 3136 and 3185 cm−1 are attributed to water stretching vibrations. By using a Libowitzky empirical function, hydrogen bond distances are calculated from the OH stretching wavenumbers. Strong hydrogen bonds in the structure of ludlamite are observed as determined by their hydrogen bond distances. The application of infrared and Raman spectroscopy to the study of ludlamite enables the molecular structure of the pegmatite mineral ludlamite to be assessed.

A vibrational spectroscopic study of the phosphate mineral zanazziite - Ca2(MgFe2+)(MgFe2+Al)4Be4(PO4)6⋅6(H2O)

Zanazziite is the magnesium member of a complex beryllium calcium phosphate mineral group named roscherite. The studied samples were collected from the Ponte do Piauí mine, located in Itinga, Minas Gerais. The mineral was studied by electron microprobe, Raman and infrared spectroscopy. The chemical formula can be expressed as Ca2.00(Mg3.15,Fe0.78,Mn0.16,Zn0.01,Al0.26,Ca0.14)Be4.00(PO4)6.09(OH)4.00⋅5.69(H2O) and shows an intermediate member of the zanazziite–greinfeinstenite series, with predominance of zanazziite member. The molecular structure of the mineral zanazziite has been determined using a combination of Raman and infrared spectroscopy. A very intense Raman band at 970 cm−1 is assigned to the phosphate symmetric stretching mode whilst the Raman bands at 1007, 1047, 1064 and 1096 cm−1 are attributed to the phosphate antisymmetric stretching mode. The infrared spectrum is broad and the antisymmetric stretching bands are prominent. Raman bands at 559, 568, 589 cm−1 are assigned to the ν4 out of plane bending modes of the PO4 and HPO4 units. The observation of multiple bands supports the concept that the symmetry of the phosphate unit in the zanazziite structure is reduced in symmetry. Raman bands at 3437 and 3447 cm−1 are attributed to the OH stretching vibrations; Raman bands at 3098 and 3256 are attributed to water stretching vibrations. The width and complexity of the infrared spectral profile in contrast to the well resolved Raman spectra, proves that the pegmatitic phosphates are better studied with Raman spectroscopy.

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.

Is chrysocolla (Cu,Al)2H2Si2O5(OH)4·nH2O related to spertiniite Cu(OH)2? - a vibrational spectroscopic study

Chrysocolla (Cu, Al)2H2Si2O5(OH)4·nH2O is a hydrated copper hydroxy silicate and is commonly known as a semi-precious jewel. The mineral has an ill defined structure but is said to be orthorhombic, although this remains unproven. Thus, one of the few methods of studying the molecular structure of chrysocolla is to use vibrational spectroscopy. Chrysocolla may be defined as a colloidal mineral. The question arises as to whether chrysocolla is a colloidal system of spertiniite and amorphous silica. The main question addressed by this study is whether chrysocolla is (1) a mesoscopic assemblage of spertiniite, Cu(OH)2, silica, and water, (2) represents a colloidal gel or (3) is composed of microcrystals with a distinct structure. Considerable variation in the vibrational spectra is observed between chrysocolla samples. The Raman spectrum of chrysocolla is characterised by an intense band at 3624 cm−1 assigned to the OH stretching vibrations. Intense Raman bands found at 674, 931 and 1058 cm−1 are assigned to SiO3 vibrations. The Raman spectrum of spertiniite does not correspond to the spectrum of chrysocolla and it is concluded that the two minerals are not related. The spectra of chrysocolla correspond to a copper silicate colloidal gel.

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.

Effect of rehydration on structure and surface properties of thermally treated palygorskite

Palygorskite has a fibrous like morphology with a distinctive layered appearance. The simplified formula of palygorskite (Mg5Si8O20(OH)2(OH2)4 nH2O) indicates that two different types of water are present. The dehydration and rehydration of palygorskite have been studied using thermogravimetry and H2O-tem- perature programmed desorption. X-ray diffractograms, NH3 adsorption profiles, and NH3 desorption profiles were obtained for thermally treated palygorskite as a function of temperature. The results proved water molecules were mainly derived from Si–OH units. In addition, five kinds of acid sites were found for palygorskite. The number of acid sites of external surfaces was larger than that of the internal sur- faces. Bonding on the internal surface acid sites was stronger than the bonding of the external surfaces. Rehydration restored the folded structure of palygorskite when thermal treatment temperature was lower than 300 oC.

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.

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.

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.

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.

Characterization of tight gas reservoir pore structure using USANS/SANS and gas adsorption analysis

Small-angle and ultra-small-angle neutron scattering (SANS and USANS) measurements were performed on samples from the Triassic Montney tight gas reservoir in Western Canada in order to determine the applicability of these techniques for characterizing the full pore size spectrum and to gain insight into the nature of the pore structure and its control on permeability. The subject tight gas reservoir consists of a finely laminated siltstone sequence; extensive cementation and moderate clay content are the primary causes of low permeability. SANS/USANS experiments run at ambient pressure and temperature conditions on lithologically-diverse sub-samples of three core plugs demonstrated that a broad pore size distribution could be interpreted from the data. Two interpretation methods were used to evaluate total porosity, pore size distribution and surface area and the results were compared to independent estimates derived from helium porosimetry (connected porosity) and low-pressure N2 and CO2 adsorption (accessible surface area and pore size distribution). The pore structure of the three samples as interpreted from SANS/USANS is fairly uniform, with small differences in the small-pore range (<2000 Å), possibly related to differences in degree of cementation, and mineralogy, in particular clay content. Total porosity interpreted from USANS/SANS is similar to (but systematically higher than) helium porosities measured on the whole core plug. Both methods were used to estimate the percentage of open porosity expressed here as a ratio of connected porosity, as established from helium adsorption, to the total porosity, as estimated from SANS/USANS techniques. Open porosity appears to control permeability (determined using pressure and pulse-decay techniques), with the highest permeability sample also having the highest percentage of open porosity. Surface area, as calculated from low-pressure N2 and CO2 adsorption, is significantly less than surface area estimates from SANS/USANS, which is due in part to limited accessibility of the gases to all pores. The similarity between N2 and CO2-accessible surface area suggests an absence of microporosity in these samples, which is in agreement with SANS analysis. A core gamma ray profile run on the same core from which the core plug samples were taken correlates to profile permeability measurements run on the slabbed core. This correlation is related to clay content, which possibly controls the percentage of open porosity. Continued study of these effects will prove useful in log-core calibration efforts for tight gas.

Dots versus antidots : computational exploration of structure, magnetism, and half-metallicity in boron−nitride nanostructures

Triangle-shaped nanohole, nanodot, and lattice antidot structures in hexagonal boron-nitride (h-BN) monolayer sheets are characterized with density functional theory calculations utilizing the local spin density approximation. We find that such structures may exhibit very large magnetic moments and associated spin splitting. N-terminated nanodots and antidots show strong spin anisotropy around the Fermi level, that is, half-metallicity. While B-terminated nanodots are shown to lack magnetism due to edge reconstruction, B-terminated nanoholes can retain magnetic character due to the enhanced structural stability of the surrounding two-dimensional matrix. In spite of significant lattice contraction due to the presence of multiple holes, antidot super lattices are predicted to be stable, exhibiting amplified magnetism as well as greatly enhanced half-metallicity. Collectively, the results indicate new opportunities for designing h-BNbased nanoscale devices with potential applications in the areas of spintronics, light emission, and photocatalysis.