1,721,847 research outputs found
Raman microscopy of selected chromate minerals
No full textA series of related chromate bearing minerals including crocoite,\ud
phoenicocroite, hemihedrite, iranite, macquartite, fornacite and vauquelinite have\ud
been analysed by Raman microscopy. These minerals are closely related and often\ud
have related paragenesis. Raman microscopy enables the selection of individual\ud
crystals of these minerals for Raman spectroscopic analysis. This is of importance as\ud
often the crystals are found adjacent to each other in the same matrix through\ud
paragenetic relationships. The Raman spectrum of crocoite shows three bands in the\ud
CrO4 stretching region at 856, 841 and 825 cm-1, phoenicocroite at 856, 848, 839 and\ud
826 cm-1, hemihedrite at 847, 837 and 824 cm-1, iranite bands at 865, 846 and 818\ud
cm-1, macquartite at 857, 840 and 814 cm-1. The Raman spectra of fornacite and\ud
vauquelinite are complicated by the presence or AsO4 and PO4 units in the structure\ud
and often the spectra are broad and vary with chemical composition. A comparison of\ud
the spectra of these minerals is made with that of the hexavalent chromate mineral\ud
edoylerite. Raman microscopy is a powerful and underutilized technique in terms of\ud
mineralogy for the study of closely related minerals such as these chromate minerals
Raman and infrared spectroscopy of arsenates of the roselite and fairfieldite mineral subgroups
No full textRaman spectroscopy complimented with infrared spectroscopy has been used to determine the molecular structure of the roselite arsenate minerals of the roselite and fairfieldite subgroups of formula Ca2B(AsO4)2.2H2O (where B may be Co, Fe2+, Mg, Mn, Ni, Zn). The Raman arsenate (AsO4)2- stretching region shows strong differences between the roselite arsenate minerals which is attributed to the cation substitution for calcium in the structure. In the infrared spectra complexity exists with multiple (AsO4)2- antisymmetric stretching vibrations observed, indicating a reduction of the tetrahedral symmetry. This loss of degeneracy is also reflected in the bending modes. Strong Raman bands around 450 cm-1 are assigned to ν4 bending modes. Multiple bands in the 300 to 350 cm-1 region assigned to ν2 bending modes provide evidence of symmetry reduction of the arsenate anion. Three broad bands for roselite are found at 3450, 3208 and 3042 cm-1 and are assigned to OH stretching bands. By using a Libowitzky empirical equation hydrogen bond distances of 2.75 and 2.67 Å are estimated. Vibrational spectra enable the molecular structure of the roselite minerals to be determined and whilst similarities exist in the spectral patterns, sufficient differences exist to be able to determine the identification of the minerals
Raman spectroscopy of natural oxalates
No full textOxalates are markers or indicators of environmental events. Oxalates are readily determined by Raman spectroscopy. Thus deterioration of works of art, biogeochemical cycles, plant metal complexation, the presence of pigments and minerals formed in caves can be analysed. A comparative study of a suite of natural oxalates including weddellite, whewellite, moolooite, humboldtine, glushinskite, natroxalate and oxammite has been undertaken using Raman spectroscopy. The minerals are characterised by the wavenumber of the CO stretching vibration which is cation sensitive. The band is observed at 1468 cm-1 for weddellite, 1489 cm-1 for moolooite, 1471 cm-1 for glushinskite and 1456 cm-1 for natroxalate. Except for oxammite, the infrared and Raman spectra are mutually exclusive indicating that the minerals are bidentate. Differences are also observed in the wavenumber of the water OH stretching bands of the minerals. The significance of this work rests with the ability of Raman spectroscopy to identify oxalates which often occur as films on a host rocks or works of art
An infrared and Raman spectroscopic study of the uranyl micas
No full textVibrational spectroscopy using a combination of infrared and Raman spectroscopy has been used to study the uranyl micas also known as the autunite minerals, of general formula M(UO2)2(XO4)2.8-12H2O where M may be Ba, Ca, Cu, Fe2+, Mg, Mn2+ or ½(HAl) and X is As, or P. Included in these minerals are autunite, metautunite, torbernite, metatorbernite, metazeunerite, saléeite and sabugalite. Compared with the results of infrared spectroscopy, Raman microscopy shows excellent band separation enabling the separation and identification of bands attributed to (UO2)2+ units, PO4 and AsO4 units. Common to all spectra were bands at around 900 and 818 cm-1, attributed to the antisymmetric and symmetric stretching vibrations of the (UO2)2+ units. Water in autunites is in a highly structured arrangement in the interlayer of the uranyl micas. Water molecules are differentiated according to the strength of the hydrogen bonds formed between the water and the adjacent uranyl-phosphate or uranyl-arsenate surfaces and the hydration sphere of the interlayer cation
An infrared spectroscopic study of the some Autunite minerals
No full textA series of selected autunites with phosphate as the anion have been studied using infrared spectroscopy. Each autunite mineral has its own characteristic spectrum. The spectra for different autunites with the same composition are different. It is proposed that this difference is due to the structure of water and hydrated cations in the interlayer region between the uranyl phosphate sheets. This structure is different for different autunites. The position of the water hydroxyl stretching bands is related to the strength of the hydrogen bonds as determined by hydrogen bond distance. The highly ordered structure of water is also observed in the water HOH bending modes where a high wavenumber bands are observed. The phosphate and uranyl stretching vibrations overlap and are obtained by curve resolution
Raman spectroscopy of selected copper minerals of significance in corrosion
No full textThe Raman spectroscopy of selected minerals of the corrosion products has been measured including nantokite, eriochalcite, claringbullite, atacamite, paratacamite, clinoatacamite and brochantite and related minerals. The free energy of formation shows that each mineral is stable relative to copper metal. The mineral, which is formed in copper corrosion, depends on the kinetics and conditions of the reaction. Raman spectroscopy clearly identifies each mineral by its characteristic Raman spectrum. The Raman spectrum is related to the mineral structure and bands are assigned to CuCl stretching and bending modes and to SO stretching modes. Clinoatacamite is identified as the polymorph of atacamite and not paratacamite. Paratacamite is a separate mineral with a similar but different structure to that of atacamite
Optical absorption and EPR studies on tenorite mineral
No full textOptical absorption and EPR studies of the mineral tenorite, a cupric oxide, which originated from Mexico and contains 54.40 wt% of CuO. EPR spectral results indicate two Cu(II) closely interacting ions to give a d2 type structure. The calculated spin Hamiltonian at Rt and LNT are g = 2.160 and D = 125 G . The intensity of resonance line is not the same in low and high field regions. The optical absorption spectrum is due to Cu(II) which three sets of energies indicating Cu(II) in two independent tetragonal C4v symmetry, in addition to d2 structure of octahedral coordination. The octahedral and tetragonal field parameters are compared with those reported for several other copper containing minerals
A Raman spectroscopic study of selected minerals of the rosasite group
No full textMinerals in the rosasite mineral group namely rosasite, glaucosphaerite, kolwezite, mcguinnessite, nullaginite and pokrovskite have been studied by Raman spectroscopy at 298 and 77 K and complimented with infrared spectroscopy. The spectral patterns for the minerals rosasite, glaucosphaerite, kolwezite and mcguinnessite are similar to that of malachite implying the structure is the same as malachite i.e. monoclinic. A comparison is made with the spectra of malachite. The symmetry of the carbonate anion in the rosasite mineral group is C2v or Cs and is composition dependent. Two (CO3)2- symmetric stretching modes are observed for the rosasite minerals at 1060 and 1090 cm-1. Two hydroxyl stretching modes are observed for the rosasite mineral group. The position of these bands is determined to be a function of the hydrogen bond lengths. Hydrogen bond distances for rosasite are calculated as 2.867, 2.799 and 2.780 Å whereas for pokrovskite the distances are 3.280 and 2.999 Å. The effect of lowering the temperature from ambient to 77 K results in a decrease of the hydrogen bond distances by 5%. Multiple Raman bands are observed in the 800 to 850 cm-1 and the 720 to 750 cm-1 regions and are attributed to ν2 and ν4 bending modes confirming the reduction of the carbonate anion in the rosasite structure
Vibrational spectroscopic study of the antimonate mineral bindheimite Pb2Sb2O6(O,OH)
No full textRaman spectroscopy complimented with infrared spectroscopy has been used to characterise the antimonate mineral bindheimite Pb2Sb2O6(O,OH). The mineral is characterised by an intense Raman band at 656 cm-1 assigned to SbO stretching vibrations. Other lower intensity bands at 664, 749 and 814 cm-1 are also assigned to stretching vibrations. This observation suggests the non-equivalence of SbO units in the structure. Low intensity Raman bands at 293, 312 and 328 cm-1 are assigned to the OSbO bending vibrations. Infrared bands at 979, 1008, 1037 and 1058 cm-1 may be assigned to δ OH deformation modes of SbOH units. Infrared bands at 1603 and 1640 cm-1 are assigned to water bending vibrations, suggesting that water is involved in the bindheimite structure. Broad infrared bands centred upon 3250 cm-1 supports this concept. Thus the true formula of bindheimite is questioned and probably should be written as Pb2Sb2O6(O,OH,H2O
- …
