Electronic And Vibrational Spectra of Mn Rich Sursassite

The optical spectrum of Mn2+ in octahedral coordination for sursassite is characterized by well resolved bands at 580, 515, 470, 390, 340, and 295 nm (17240, 19420, 21280, 25640, 29410 and 33900 cm-1). Crystal field parameters evaluated from the observed bands are Dq = 690, B = 680 and C = 2800 cm-1. A broad band centred around 13000 cm-1 attributed to Fe(III) ion is an impurity in sursassite confirmed from EDX analysis. Vibrational spectra have been investigated both by IR and Raman spectroscopy. The correlation between vibrational modes and the structural properties of the manganese silicate, sursassite, is made and compared with other silicates. Two vibrational modes of CO32- observed; the antisymmetric stretching mode (￮3) at 1420 cm-1 (IR active) and the out-of-plane bending mode ( ￮2) (IR and Raman active) at ~875 cm-1. This confirms the Mn rich phases in sursassite as observed from SEM probably a Mn carbonate-rhodochrosite

Spectroscopic study of chromium, iron, OH, fluid and mineral inclusions in uvarovite and fuchsite

12 páginas, 10 figurasOctahedrally-coordinated Cr3+ possesses peculiar spectral features which made easy to identify it in minerals, even in minor amounts. Chromium has been studied in uvarovite and fuchsite by optical and EPR spectra. Optical, EPR, FT-infrared and EPMA studies have also let to determine the presence of Fe3+ and Ti3+ and fluid inclusions within uvarovite and fuchsite. Absorption and scattering effects on the optical spectra obtained for Cr-bearing samples, resulting from the presence of inclusions, are also discussed in this work.This work was financed by Research Project BT2000-0582 (S.E.U.I.D.-M.C.T., Spain)Peer reviewe

Spectroscopic characterization of rosaite and aurichalcite

15 páginas, 8 figurasChemical and textural studies show fibrous rosasite crystals, with a spread Cu : Zn ratio, occuring in a calcite matrix together with goethite, psilomelane, quartz and saponite in oxidation zones of copper ore deposits. Aurichalcite occurs also as fibrous crystals and has a more fixed composition (Cu : Zn ratio is 1.3 : 3.7). Aurichalcite sample also contains prismatic hemimorphite. The nature of the copper ion and its site symmetry in rosasite and aurichalcite were investigated using a combination of optical absorption and EPR spectroscopy. Optical absorptions of rosasite exhibited three bands due to Cu2+ in tetragonally elongated octahedral site and the parameters evaluated from the observed band positions are Dq = 1480, Ds = 2330 and Dt = 410cm-1. The EPR features observed in rosasite (g > g||) is an indication of predominant interactions within the copper ions (Cu Zn). Optical and EPR spectra of aurichalcite sample account for Cu2+ ion in the distorted octahedron site. The molecular structures of the two copper zinc carbonate hydroxide minerals were also studied by FTIR spectroscopy. The infrared spectra of the two minerals are different in line with differences in crystal structure and composition. The shift towards lower wave numbers of the carbonate bands and splitting of bands are more in aurichalcite than the other. This indicates that the symmetry of CO32- ion in both the minerals is lowered from D3h to C2v or Cs and distortion is more in aurichalcite.This work was financed by Research Project BT2000-0582 (S.E.U.I:D.-M.C.T., Spain)Peer reviewe

Synthesis and spectroscopic characterisation of aurichalcite (Zn,Cu2+)5(CO3)2(OH)6 -implications for Cu-ZnO catalysts

The Cu-ZnO catalysts with variable Cu/Zn ratio, between Zn-rich and Cu-rich compositions have been investigated by a combination of electronic and vibrational spectra. Synthesized catalysts exhibit two d-d transition bands of Cu2+ ions in a distorted octahedral symmetry, at 7600 and 12900 cm-1 (1315 and 775 nm). The effect of structural cations substitution (Zn2+ and Cu2+) on band shifts observed in spectra of the synthetic samples. The observation of two broad features at ~7600 and 12900 cm-1 (1315 and 775 nm) is a strong indication for Zn2+ substitution by Cu2+ ions. The result of multiple bands in the symmetric stretching and bending regions confirms the reduction of symmetry from D3h to C2v/Cs for (CO3)2- ion in aurichalcite. The synthetic aurichalcite may be used as a standard for identification of spectral properties of naturally occurring anhydrous carbonate minerals

Raman spectroscopy of hydroxy nickel carbonate minerals nullaginite and zaratite

Raman spectroscopy combined with infrared spectroscopy has been used to study the minerals, nullaginite and zaratite. Raman bands are observed at 3650, 3556 and 3309 cm-1 for nullaginite and 3609, 3516 and 3336 cm-1 for zaraitite. By using a Libowitzky type empirical function estimation of the hydrogen bond distances of the OH and water units has been made and values vary from 0.268nm to 0.332nm. Hydrogen bond distances of OH units are less than for water units. The observation of multiple asymmetric stretching and bending modes for nullaginite suggests the carbonate is strongly distorted in contrast to zaratite for which only single bands are found. Raman bands at around 935 and 980 cm-1 are assigned to OH deformation modes