B. Jagannadha Reddy

Near Infrared Spectroscopy of Aurichalcite (Zn,Cu2+)5(CO3)2(OH)6:

In this endeavour, near infrared spectroscopy studies show evidence of variable composition in aurichalcite minerals of zinc copper carbonate hydroxides. The observation of a broad feature in the electronic part of the spectrum around 11,500 cm−1 (870 nm) is a strong indication of Cu2+ substitution for Zn2+ in the mineral. Overtones of OH vibrations in the spectra from 7250 to 5400 cm−1 (1380–1850 nm) show strong hydrogen bonding in these carbonates. A band common to spectra of all carbonates appears near 5400 cm−1 (1850 nm) due to the combination of both OH-stretching and HOH-bending vibrations, which may be attributed to adsorbed water. Aurichalcite minerals display a spectral sequence of five absorption bands with variation of both band positions and intensities and this is the chief spectral feature observed in the range 5200–5100 cm−1 (1920–2380 nm) due to vibrational processes of the carbonate ion. The frequency shift of carbonate bands suggests the effect of divalent cations and/or variations of the Zn/Cu ratio in aurichalcite minerals.

Characterisation of red mud by UV-vis-NIR spectroscopy.

The characterisation of red mud has been studied by diffuse reflectance spectroscopy in the UV-vis-NIR region (DRS). For the first time the ferric ion responsible for the bands has been identified from electronic spectroscopy. It contains valuable amounts of oxidised iron (Fe(3+)) and aluminium hydroxide. The NIR peak at around 11,630 cm(-1) (860 nm) with a split of two components and a pair of sharp bands near 500 nm (20000 cm(-1)) in the visible spectrum are attributed to Fe(3+) ion in distorted sixfold coordinations. The observation of identical spectral patterns (both electronic and vibrational spectra) of red mud before and after seawater neutralisation (SWN) confirmed that there is no effect of seawater neutralisation on structural cation substitutions such as Al(3+), Fe(3+), Fe(2+), Ti(3+), etc.

Structure of selected basic zinc/copper (II) phosphate minerals based upon near-infrared spectroscopy : implications for hydrogen bonding

The NIR spectra of reichenbachite, scholzite and parascholzite have been studied at 298 K. The spectra of the minerals are different, in line with composition and crystal structural variations. Cation substitution effects are significant in their electronic spectra and three distinctly different electronic transition bands are observed in the near-infrared spectra at high wavenumbers in the 12,000-7600 cm(-1) spectral region. Reichenbachite electronic spectrum is characterised by Cu(II) transition bands at 9755 and 7520 cm(-1). A broad spectral feature observed for ferrous ion in the 12,000-9000 cm(-1) region both in scholzite and parascholzite. Some what similarities in the vibrational spectra of the three phosphate minerals are observed particularly in the OH stretching region. The observation of strong band at 5090 cm(-1) indicates strong hydrogen bonding in the structure of the dimorphs, scholzite and parascholzite. The three phosphates exhibit overlapping bands in the 4800-4000 cm(-1) region resulting from the combinations of vibrational modes of (PO(4))(3-) units.

Near infrared spectroscopy of the smithsonite minerals

The importance of NIR spectroscopy has been successfully demonstrated in the present study of smithsonite minerals. The fundamental observations in the NIR spectra, in addition to the anions of OH− and CO32–, are Fe and Cu in terms of cation content. These ions exhibit broad absorption bands ranging from 13,000 cm−1 to 7000 cm−1 (770 nm to 1430 nm). One broad diagnostic absorption feature centred at 9000 cm−1 (1110 nm) is the result of ferrous ion spin allowed transition, (5T2g → 5Eg). The splitting of this band (> 1200 cm−1) is a common feature in all the spectra of the studied samples. The light green coloured sample from Namibia show two Cu(II) bands in NIR at 8050 cm−1 and 10,310 cm−1 (1240 nm and 970 nm) assigned to 2B1g → 2A1g and 2B1g → 2B2g transitions. The effects of structural cations substitution (Ca2+, Fe2+, Cu2+, Cd2+ and Zn2+) on band shifts in the electronic spectral region of 11,000 cm−1 to 7500 cm−1 (910 nm to 1330 nm) and vibrational modes of OH− and CO32– anions in the 7300 cm−1 to 4000 cm−1 (1370 nm to 2500 nm) region were used to distinguish between the smithsonites.

A near-infrared spectroscopic study of the phosphate mineral pyromorphite Pb5(PO4)3Cl.

Spectral properties as a function composition are analysed for a series of selected pyromorphite minerals of Australian origin. The minerals are characterised by d-d transitions in NIR from 12,000 to 8000 cm(-1) (0.83-1.25 microm). A broad signal observed at approximately 10,000cm(-1) (1.00 microm) is the result of ferrous ion impurity in pyromorphites and follows a relationship between band intensity in the near-infrared spectra and ferrous ion concentration. The iron impurity causes a change in colour from green-yellow to brown in the pyromorphite samples. The observation of overtones of the OH(-) fundamentals, confirms the presence OH(-) in the mineral structure. The contribution of water-OH overtones in the NIR at 5100 cm(-1) (1.96 microm) is an indication of bonded water in the minerals of pyromorphite. Spectra in the mid-IR show that pyromorphite is a known mixed phosphate and arsenate complex, Pb5(PO4,AsO4)3Cl. A series of bands are resolved in the infrared spectrum of pyromorphite at 1017, 961 and 894 cm(-1). The first two bands are assigned to nu(3), the antisymmetric stretching mode and the third band at 894 cm(-1) is the symmetric mode of the phosphate ion. Similar patterns are shown by other pyromorphite samples with variation in intensity. The cause of multiple bands near 800 cm(-1) is the result of isomorphic substitution of (PO4)(3-) by (AsO4)(3-) and the spectral pattern relates to the chemical variability in pyromorphite. The presence of (AsO4)(3-) is significant in certain pyromorphite samples.

An application of near infrared spectroscopy to the study of carbonate minerals–smithsonite, rhodochrosite, sphaerocobaltite and cadmium smithsonite

Near infrared (NIR) spectroscopy has been applied to the study of selected calcite group minerals including smithsonite, rhodochrosite, sphaerocobaltite and cadmium smithsonite. The isomorphic substitution of calcium in calcite group minerals by divalent cations such as Fe, Cu, Cd, Mn, Mg, Co, Zn is in agreement with variable spectral properties observed through NIR spectroscopy. This substitution results in highly-coloured minerals. The NIR spectra of calcite group minerals that contain absorption features due to the divalent cations, Fe2+, Cu2+ and Co2+ act as an aid to mineral identification. The main indicator is the strength of ferrous ion bands in the NIR spectra supporting spectral classification of calcite group minerals. The observation of Cu2+ bands in smithsonite and cadmium smithsonite with different band positions around 12400 and 8500 cm−1 (0.81–1.18 μm) confirms Cu2+ substitution for Zn2+. Co2+ is the major cation in sphaerocobaltite and exhibits a strong feature from 12000 to 7000 cm−1 (0.83–1.43 μm) which is distinctly different from other minerals of the group. The broad band centred at 9835 cm−1 (1.02 μm) with a split component at 8186 cm−1 (1.22 μm) is assigned to 4T1g(F) → 4T2g(F) spin-allowed transition of Co2+ ion. Significant shifts are observed for carbonate ion due to the wide range of cation substitutions in the mineral structure in conjunction with the ferrous iron which is a common impurity in calcite minerals. This NIR spectral features enable mineral identification. The implication is that NIR spectroscopy can be used to remotely detect carbonate minerals and assess their isomorphic substitution.

Optical absorption spectrum of iron in beryl

Abstract The optical absorption spectrum of Fe 3 in beryl has been studied at room and liquid air temperatures. The cubic field approximation with Dq = 1320 cm −1 , B = 720 cm −1 and C = 4.4 B is found to give a good fit to the observed band positions.

Characterisation of Ni silicate-bearing minerals by UV-vis-NIR spectroscopy Effect of Ni substitution in hydrous Ni-Mg silicates

Three Ni silicate-bearing pimelite, nepouite and pecoraite minerals, from Australia have been investigated by UV-vis-NIR spectroscopy to study the effect of Ni-Mg substitution. The observation of three major absorption bands at 9205-9095, 15,600-15,190 and 26,550-25,660 cm(-1) are the characteristic features of Ni(2+) in sixfold coordination. The effect of cation substitution like Mg(2+) for Ni(2+) on band shifts in electronic and vibrational spectra enable the distinction between the Ni-bearing silicates.

Raman spectroscopic study of the uranyl titanate mineral betafite (Ca,U)2(Ti,Nb)2O6(OH): effect of metamictization

Raman spectra of the uranyl titanate mineral betafite were obtained and related to the mineral structure. A comparison is made with the spectra of uranyl oxyhydroxide hydrates. Observed bands are attributed to the (UO2)2+ stretching and bending vibrations, U–OH bending vibrations and H2O and (OH)− stretching, bending and libration modes. U–O bond lengths in uranyls and O−H···O bond lengths are calculated from the wavenumbers assigned to the stretching vibrations. Raman bands of betafite are comparable with those of the uranyl oxyhydroxides. The mineral betafite is metamict as is evidenced by the intensity of the UO stretching and bending modes being of lower intensity than expected and by bands that are significantly broader.

An application of near infrared spectroscopy to the study of the selenite minerals: chalcomenite, clinochalcomenite and cobaltomenite

The selection of five naturally occurring selenite minerals that contain two different transition metal ions, Cu2+ and Co2+ could be distinguished by near infrared spectroscopy. Dependence of composition on spectral properties is a key to mineral identification and differentiation of the members of the selenite group. The nature of the band positions and splitting of band components in the electronic spectra of Cu2+ selenites in the region 12,400–8000 cm−1 are in conformity with octahedral geometry distortion. The two split components which are observed for the Co2+ band near 9000 cm−1 in cobaltomenites are considered as the vibrational satellites of spin-allowed transition 4T1g(F)→4T2g(F). Bands observed at 6950 cm−1, 6810 cm−1 and 6700 cm−1 are the overtones of OH stretches of structural water in selenites and a strong absorption feature near 6700 cm−1 is the result of hydrogen bonding between (SeO3)2– and H2O. These bands are shifted in cobaltomenites. A sharp absorption band at 5170 cm−1 is a common feature in all the spectra of selenite minerals and is the contribution by the combinations of the OH vibrations of water molecules, ν3 and ν1. A series of overlapping bands around 4500 and 4100 cm−1 is the result of the combination of the vibrational modes of (SeO3)2– ion in the minerals.