B.J. Reddy

Optical and EPR investigations on smithsonite minerals

Optical and EPR investigations have been made on two smithsonite (ZnCO3) minerals, one originating from the USA and the other from the UK. The optical spectra reveal the existence of Cu(II) as impurity in both the samples; and site symmetry for Cu(II) is confirmed to be tetragonally distorted octahedral. The intensity of absorption bands observed in the region 600–1200 nm in the USA sample is much stronger indicating that the impurity of Cu(II) is more in the USA sample than that in the UK sample. From EPR spectra the axial g values are determined to be g ‖ = 2.337 and g ⊥ = 2.087, which are compatible with the distorted octahedral symmetry. In addition, Mn(II) impurity is also detected in the EPR spectra of both the samples.

Electronic and vibrational spectra of gaspeite

Visible, near-infrared, IR and Raman spectra of magnesian gaspeite are presented. Nickel ion is the main source of the electronic bands as it is the principal component in the mineral where as the bands in IR and Raman spectra are due to the vibrational processes in the carbonate ion as an entity. The combination of electronic absorption and vibrational spectra (including near-infrared, FTIR and Raman) of magnesian gaspeite are explained in terms of the cation co-ordination and the behaviour of CO32– anion in the Ni–Mg carbonate. The electronic absorption spectrum consists of three broad and intense bands at 8130, 13160 and 22730 cm–1 due to spin-allowed transitions and two weak bands at 20410 and 30300 cm–1 are assigned to spin-forbidden transitions of Ni2+ in an octahedral symmetry. The crystal field parameters evaluated from the observed bands are Dq = 810; B = 800 and C = 3200 cm–1. The two bands in the near-infrared spectrum at 4330 and 5130 cm–1 are overtone and combination of CO32– vibrational modes. For the carbonate group, infrared bands are observed at 1020 cm–1(1 ), 870 cm–1 (2), 1418 cm–1 (3) and 750 cm–1 (4), of which3, the asymmetric stretching mode is most intense. Three well resolved Raman bands at 1571, 1088 and 331 cm–1 are assigned to 3, 1 and MO stretching vibrations.

Spectral Studies of Divalent Copper in Antlerite Mineral

Electron paramagnetic resonance (EPR) spectra on antlerite mineral are recorded both at RT & LNT. Optical absorption spectra are recorded from 200 - 2500 nm at RT. The chemical analysis of antlerite reveals that the concentration of CuO in the mineral is 67.30 wt%. Optical absorption spectrum of antlerite shows four bands, which are mainly due to Cu(II). EPR and optical results of the antlerite sample confirmed that Cu(II) is in rhombically distorted (D 2h ) octahedral symmetry with g 1 = 2.36, g 2 = 2.16 and g 3 = 2.07. The NIR spectra of antlerite are attributed to water fundamentals.

Spectral investigations on melanterite mineral from France

EPR, Optical and IR spectral studies on a naturally occurring mineral melanterite are carried out at room temperature. EPR studies indicate the presence of Cu(II) ion in tetragonally distorted octahedral site and hyperfine lines could not be resolved due to higher concentration of the paramagnetic impurity in the mineral. Optical absorption spectrum is a characteristic of Fe(II) and Cu(II) ions. Crystal field parameters are evaluated. IR spectrum confirms the presence of water and sulphate ions.

Mössbauer, optical absorption and EPR spectra of Fe3+ in plumbo-jarosite minerals

Abstract Mossbauer spectrum of plumbo-jarosite mineral from Utah showed the presence of Fe(III) in a distorted octahedron. EPR investigations of the sample further confirmed that ferric iron is in a distorted octahedron. The optical absorption spectrum consists of a series of bands that can be assigned to spin-forbidden crystal field transitions of Fe(III) in octahedral coordination.

X-ray powder diffraction, DTA and vibrational studies of CdNH4PO4.6H2O crystals

Cadmium Ammonium Phosphate Hexahydrate (CAPH) is analogous to naturally occurring struvite. CAPH crystals are grown by slow evaporation technique. These crystals are characterised by X-ray, TG-DTA and Infra-red studies. Powder X-ray pattern indicates the orthorhombic crystal structure analogous to struvite. TG-DTA analysis suggests loss of water of hydration (6H 2 O) between 113 and 391°C. Later the substance melts and only Cd remains around 780°C. Infra Red spectrum is characteristic of H 2 O, PO 4 3- and NH 4 + radicals.

Electron paramagnetic resonance, NIR studies on zoisite, clinozoisite and chrom-zoisite minerals

A zoisite group of mineral samples from different localities are used in the present study. An EPR study on powdered samples confirms the presence of Mn(II), Fe(III) and Cr(III) in the minerals. NIR studies confirm the presence of these ions in the minerals.

EPR, UV-visible and near infrared spectroscopic characterization of dolomite

Dolomite mineral samples having white and light green colors of Indian origin have been characterized by EPR, optical, and NIR spectroscopy. The optical spectrum exhibits a number of electronic bands due to presence of Fe(III) ions in the mineral. From EPR studies, the parameters of for Fe(III) and , and for Mn(II) are evaluated and the data confirm that the ions are in distorted octahedron. Optical absorption studies reveal that Fe(III) is in distorted octahedron. The bands in NIR spectra are due to the overtones and combinations of water molecules. Thus EPR and optical absorption spectral studies have proven useful for the study of the solid state chemistry of dolomite.

Optical absorption and EPR spectra of fuchsite.

Chromium containing mica is called fuchsite. Fuchsite originating from the Nellore district of India containing 3.37 wt.% of chromium is used in the present study. Optical absorption and EPR studies were carried out at room temperature (RT). The optical absorption spectrum gives energies at 14925, 15070, 15715, 16400, 17730 and 21740 cm(-1), which are attributed to spin-allowed transitions for Cr(3+) in an octahedral symmetry. EPR spectra show a strong resonance with g=1.98 along with two sets of weak resonances which are attributed to two sets of chromium in the sample. The zero field splitting parameter (D) is almost zero. These spectra are due to Cr(3+) in the mineral. The NIR spectrum is due to hydroxyl ions in the sample.

Spectral studies of Mn2+ in friedelite

Abstract Optical and EPR spectra of Mn 2+ in friedelite are studied both at room and low temperatures. Optical spectrum of sample exhibits four bands in UV-VIS region at room temperature. At low temperature three more bands are observed in the higher energy side. The assignments of the bands are made with the help of Tanabe-Sugano diagram drawn for d 5 configuration with C / B = 5. The EPR spectrum of Mn 2+ in the sample gives a single peak with g = 1.97.