Navegando por Autor "Menezes Filho, Luiz Alberto Dias"

Agora exibindo 1 - 5 de 5

Pauloabibite, trigonal NaNbO3, isostructural with ilmenite, from the Jacupiranga carbonatite, Cajati, São Paulo, Brazil.
(2015) Menezes Filho, Luiz Alberto Dias; Atencio, Daniel; Andrade, Marcelo Barbosa de; Downs, Robert T.; Chaves, Mario Luiz de Sá Carneiro; Romano, Antônio Wilson; Persiano, Aba Israel Cohen
Pauloabibite (IMA 2012-090), trigonal NaNbO3, occurs in the Jacupiranga carbonatite, in Cajati County, São Paulo State, Brazil, associated with dolomite, calcite, magnetite, phlogopite, pyrite, pyrrhotite, ancylite-(Ce), tochilinite, fluorapatite, “pyrochlore”, vigezzite, and strontianite. Pauloabibite occurs as encrustations of platy crystals, up to 2 mm in size, partially intergrown with an unidentified Ca-Nb-oxide, embedded in dolomite crystals, which in this zone of the mine can reach centimeter sizes. Cleavage is perfect on {001}. Pauloabibite is transparent and displays a sub-adamantine luster; it is pinkish brown and the streak is white. The calculated density is 4.246 g/cm3 . The mineral is uniaxial; n(mean)calc is 2.078. Chemical composition (n = 17, WDS, wt%) is: Na2O 16.36, MgO 0.04, CaO 1.36, MnO 0.82, FeO 0.11, SrO 0.02, BaO 0.16, SiO2 0.03, TiO2 0.86, Nb2O5 78.66, Ta2O5 0.34, total 98.76. The empirical formula is (Na0.88Ca0.04Mn2+ 0.02)S0.94(Nb0.98Ti0.02)S1.00O3. X-ray powder-diffraction lines (calculated pattern) [d in Å(I)(hkl)] are: 5.2066(100)(003), 4.4257(82)(101), 3.9730(45)(012), 2.9809(54) (104), 2.3718(88)(213), 1.9865(28)(024), 1.8620(53)(216), and 1.5383(30)(300). It is trigonal, space group: R3, a = 5.3287(5), c = 15.6197(17) Å, V = 384.10(7) Å3 , Z = 6. The crystal structure was solved (R1 = 0.0285, wR2 = 0.0636 for 309 observed reflections). Pauloabibite is isostructural with ilmenite and is polymorphic with isolueshite (cubic) and lueshite (orthorhombic). The name is in honor of Paulo Abib Andery (1922–1976).
Raman and infrared spectroscopic characterization of beryllonite, a sodium and beryllium phosphate mineral - implications for mineral collectors.
(2012) Frost, Ray Leslie; Xi, Yunfei; Cipriano, Ricardo Augusto Scholz; Belotti, Fernanda Maria; Menezes Filho, Luiz Alberto Dias
The mineral beryllonite has been characterized by the combination of Raman spectroscopy and infrared spectroscopy. SEM–EDX was used for the chemical analysis of the mineral. The intense sharp Raman band at 1011 cm_1, was assigned to the phosphate symmetric stretching mode. Raman bands at 1046, 1053, 1068 and the low intensity bands at 1147, 1160 and 1175 cm_1 are attributed to the phosphate antisymmetric stretching vibrations. The number of bands in the antisymmetric stretching region supports the concept of symmetry reduction of the phosphate anion in the beryllonite structure. This concept is supported by the number of bands found in the out-of-plane bending region. Multiple bands are also found in the in-plane bending region with Raman bands at 399, 418, 431 and 466 cm_1. Strong Raman bands at 304 and 354 cm_1 are attributed to metal oxygen vibrations. Vibrational spectroscopy served to determine the molecular structure of the mineral. The pegmatitic phosphate minerals such as beryllonite are more readily studied by Raman spectroscopy than infrared spectroscopy.
Spectroscopic characterization of transition metal impurities in natural montebrasite/amblygonite.
(2010) Dias, Lorena Nunes; Pinheiro, Mauricio Veloso Brant; Moreira, Roberto Luiz; Krambrock, Klaus Wilhelm Heinrich; Guedes, Kassílio José; Menezes Filho, Luiz Alberto Dias; Karfunkel, Joachim; Schnellrath, Jurgen; Cipriano, Ricardo Augusto Scholz
Natural single-crystal specimens of the montebrasite/amblygonite series from Brazil, with general formula LiAlPO4(F,OH), were investigated by electron microprobe, Raman spectroscopy, X-ray diffraction, and infrared absorption. Since little is known about impurities and their local symmetries, electron paramagnetic resonance (EPR) was applied. Six different paramagnetic impurities and radiation defects were detected by EPR. Three of them, all substituting for Al3+ ions, namely, iron (Fe3+), vanadium (V4+), and niobium (Nb4+) impurities were characterized in this work. The Fe3+ (3d5)-related EPR spectra and angular dependencies show occupation of low-symmetry sites that are revealed in the high asymmetry parameter of the electronic fine structure, E/D = 0.27. Vanadium and niobium impurities are identified through their typical strong hyperfine interactions. Both form interesting examples for which the properties of 3d1 ion (V4+) and 4d1 ion (Nb4+) in the same host matrix can be compared. It is shown that both ions form complex defects of type VO2+ (vanadyl) and NbO2+ (niobyl), showing superhyperfine interaction with two equivalent hydrogen ions and not to fluorine. The EPR rotation patterns are analyzed in detail for three mutually perpendicular crystal planes. Spin Hamiltonian parameters are calculated and discussed.
A vibrational spectroscopic study of the phosphate mineral zanazziite Ca2(MgFe2+)(MgFe2+Al)4Be4(PO4)6 6(H2O).
(2013) Frost, Ray Leslie; Xi, Yunfei; Cipriano, Ricardo Augusto Scholz; Belotti, Fernanda Maria; Menezes Filho, Luiz Alberto Dias
Zanazziite is the magnesium member of a complex beryllium calcium phosphate mineral group named roscherite. The studied samples were collected from the Ponte do Piaui 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 m4 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.
Wilancookite, (Ba,K,Na)8(Ba,Li,[])6Be24P24O96·32H2O, a new 2 beryllophosphate with a zeolite framework.
(2017) Hatert, Frédéric; Philippo, Simon; Ottolini, Luisa; Bol, Fabrice Dal; Cipriano, Ricardo Augusto Scholz; Chaves, Mario Luiz de Sá Carneiro; Yang, Hexiong; Downs, Robert T.; Menezes Filho, Luiz Alberto Dias
Wilancookite, ideally (Ba,K,Na)8(Ba,Li,[])6Be24P24O96·32H2O, is a new mineral species from the Lavra Ponte do Piauí 19 complex granitic pegmatite, Minas Gerais, Brazil. It occurs as tiny dodecahedral {1 1 0} crystals, deposited on moraesite fibres. 20 Associated primary minerals are albite, montebrasite, Li-bearing micas, cassiterite, elbaite and quartz, while the secondary phosphate 21 association contains fluorapatite, childrenite, eosphorite, zanazziite, greifenstenite, guimarãesite, ushkovite, saléeite and moraesite. 22 The mineral is transparent and colourless, with a vitreous lustre; it is non-fluorescent, brittle, and its streak is white. The estimated 23 Mohs hardness is 4–5, and the calculated density is 3.05 g/cm3.Wilancookite is isotropic, colourless, non-pleochroic, with n = 1.560(2) 24 (measured under l = 590nm). Electron- and ion-microprobe analyses give (in wt%): P2O5 36.19, SiO2 0.04, Al2O3 0.41, BaO 25 34.65, Na2O 0.09, K2O 0.32, BeO 12.86, Li2O 0.50, and H2Ocalc 12.31, total 97.37wt%. The resulting empirical formula, calculated 26 on the basis of 96 anhydrous oxygen atoms, is (Ba7.54K0.32Na0.14)S8.00(Ba3.04Li1.57[]1.39)S6.00Be24.08(P23.88Al0.38Si0.03)S24.29 27 O96·32H2O. The single-crystal unit-cell parameters are a = 13.5398(2)A and V = 2482.21(7), space group I23. The eight strongest 28 lines in the powder X-ray diffraction pattern [d(in A )(I)(hkl)] are: 6.90(60)(2 0 0), 5.54(80)(2 1 1), 3.630(60)(3 2 1, 3 1 2), 3.212(70) 29 (3 3 0, 4 1 1), 3.043(100)(4 2 0, 4 0 2), 2.885(70)(3 3 2), 2.774(80)(4 2 2), and 2.398(60)(4 4 0). The crystal structure of wilancookite 30 has been refined, based on single-crystal X-ray diffraction data, to R1 = 4.58%; the beryllophosphate framework is similar to that 31 occurring in pahasapaite, and is based on zeolite-RHO cages. The mineral species and name were approved by the Commission on 32 New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2015-034).