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Lecontite, (NH4)Na(SO4).2H2O, was synthesised at room temperature in high purity compared to earlier work with a minor impurity of mascagnite, (NH4)2SO4. Rietveld refinement of the XRD results confirmed the crystal structure and unit cell dimensions as published earlier. Raman and Infrared spectroscopy, in conjunction with factor group analysis, resulted in a complex pattern of overlapping sulphate, NH and OH modes. The NH modes υ1 was observed around 2880 cm−1, υ2 around 1700 cm−1 overlapping with water OH-bending modes, υ3 around 3300 cm−1 overlapping with water OH-stretching modes around 3023, 3185 and 3422 cm−1, and υ4 around 1432, 1447 and 1462 cm−1. The sulphate group in the crystal structure displays a decrease in symmetry from T d as evidenced by the activation of the ν1 mode at 982 cm−1 and the ν2 mode around 452 cm−1 in the Infrared spectrum. The υ3 mode shows clear splitting in the infrared spectra with a strong band at 1064 cm−1 accompanied by two shoulders at 1107 and 1139 cm−1. The Raman spectra show three weak bands at 1068, 1109 and 1135 cm−1 with a shoulder at 1155 cm−1. Similar splitting was observed for the υ4 mode around 611 and 632 cm−1 in the Infrared and Raman spectra, respectively. [ABSTRACT FROM AUTHOR]

Thermogravimetry combined with mass spectrometry has been used to study the thermal decomposition of a synthetic hydronium jarosite. Five mass loss steps are observed at 262, 294, 385, 557 and 619°C. The mass loss step at 557°C is sharp and marks a sharp loss of sulphate as SO3 from the hydronium jarosite. Mass spectrometry through evolved gases confirms the first three mass loss steps to dehydroxylation, the fourth to a mass loss of the hydrated proton and a sulphate and the final step to the loss of the remaining sulphate. Changes in the molecular structure of the hydronium jarosite were followed by infrared emission spectroscopy. This technique allows the infrared spectrum at the elevated temperatures to be obtained. Infrared emission spectroscopy confirms the dehydroxylation has taken place by 400 and the sulphate loss by 650°C. Jarosites are a group of minerals formed in evaporite deposits and form a component of the efflorescence. The minerals can function as cation and heavy metal collectors. Hydronium jarosite has the potential to act as a cation collector by the replacement of the proton with a heavy metal cation. [ABSTRACT FROM AUTHOR]

Abstract: Minerals in the rosasite group namely rosasite, glaucosphaerite, kolwezite, mcguinnessite have been studied by a combination of infrared and Raman spectroscopy. The spectral patterns for the minerals rosasite, glaucosphaerite, kolwezite and mcguinnessite are similar to that of malachite implying the molecular structure is similar to malachite. A comparison is made with the spectrum of malachite. The rosasite mineral group is characterised by two OH stretching vibrations at ∼3401 and 3311cm−1. Two intense bands observed at ∼1096 and 1046cm−1 are assigned to ν 1(CO3)2− symmetric stretching vibration and the δ OH deformation mode. Multiple bands are found in the 800–900 and 650–750cm−1 regions attributed to the ν 2 and ν 4 bending modes confirming the symmetry reduction of the carbonate anion in the rosasite mineral group as C 2v or C s. A band at ∼560cm−1 is assigned to a CuO stretching mode. [Copyright &y& Elsevier]

Abstract: The mineral giniite has been synthesised and characterised by XRD, SEM and Raman and infrared spectroscopy. SEM images of the olive-green giniite display a very unusual image of pseudo-spheres with roughened surfaces of around 1–10μm in size. The face to face contact of the spheres suggests that the spheres are colloidal and carry a surface charge. Raman spectroscopy proves the (PO4)3− units are reduced in symmetry and in all probability more than one type of phosphate unit is found in the structure. Raman bands at 77K are observed at 3380 and 3186cm−1 with an additional sharp band at 3100cm−1. The first two bands are assigned to water stretching vibrations and the latter to an OH stretching band. Intense Raman bands observed at 396, 346 and 234cm−1are attributed to the FeO stretching vibrations. The giniite phosphate units are characterised by two Raman bands at 1023 and 948cm−1 assigned to symmetric stretching mode of the (PO4)3− units. A complex band is observed at 460.5cm−1 with additional components at 486.8 and 445.7cm−1 attributed to the ν2 bending modes suggesting a reduction of symmetry of the (PO4)3− units. [Copyright &y& Elsevier]

Abstract: Three turquoise minerals of different origins with formula CuAl6(PO4)4(OH)8·4H2O have been studied by Raman spectroscopy at 298 and 77K and by infrared spectroscopy. A comparison of the turquoise spectra is made with the spectra of chalcosiderite. The spectra of the three mineral samples are very similar in the 1200–900cm−1 region but strong differences are observed in the 900–100cm−1 region. The effect of substitution of Fe for Al in chalcosiderite shifts the bands to lower wavenumbers. Factor group analysis (FGA) implies four OH stretching vibrations for both the water and hydroxyl units. Two bands ascribed to water are observed at 3276 and 3072cm−1 at 298K which becomes four bands at 77K. Three hydroxyl stretching vibrations are observed in the 298K spectrum and four in the 77K spectrum. Calculations using a Libowitzky type formula show that the hydrogen bond distances of the water molecules are 2.735 and 2.665Å which are considerably shorter than the values for the hydroxyl units 2.909, 2.853 and 2.840Å. Two phosphate stretching vibrations at 1066 and 1042cm−1 in line with the two independent phosphate units in the structure of turquoise. Three bands are observed at 1184, 1161 and 1106cm−1 assigned to the phosphate antisymmetric stretching vibrations. FGA predicts six bands but only three are observed due to accidental degeneracy. Both the ν 2 and ν 4 bending regions are complex with increased complexity observed in the 77K spectra. [Copyright &y& Elsevier]

Abstract: The phosphate minerals hannayite, newberyite and struvite have been studied by Raman spectroscopy using a thermal stage. Hannayite and newberyite are characterised by an intense band at around 980cm−1 assigned to the symmetric stretching vibration of the HPO4 units. In contrast the symmetric stretching mode is observed at 942cm−1 for struvite. The Raman spectra are characterised by multiple anti-symmetric stretching bands and and bending modes indicating strong distortion of the HPO4 and PO4 units. Hannayite and newberyite are defined by bands at 3382 and 3350cm−1 attributed to HOPO3 vibrations and hannayite and struvite by bands at 2990, 2973 and 2874 assigned to NH4 + bands. Raman spectroscopy has proven most useful for the analysis of these ‘cave’ minerals where complex paragenetic relationships exist between the minerals. [Copyright &y& Elsevier]

Abstract: The ability of near infrared reflectance spectroscopy to classify the rosasite group minerals from spectral characteristics is demonstrated. NIR spectroscopy can be regarded as an alternative tool for structure analysis. The spectra show that rosasite group minerals with different cations can be distinguished. Ni2+ in nullaginite [Ni2(CO3)(OH)2] is conspicuous through a single broad band absorption feature at 8525cm−1, extended from 11,000 to 7000cm−1. The effect of Ni on Cu is seen in the spectrum of glaukosphaerite [(Cu, Ni)2(CO3)(OH)2] both by a red shift of the spectrum and reduction in intensity of bands with variable positions of band maxima for Cu2+ at 6995cm−1and Ni2+ at 7865cm−1. The spectrum of rosasite [(Cu, Zn)2(CO)3(OH)2] is characterised by Cu2+ band at 7535cm−1. Kolwezite [(Cu, Co)2(CO)3(OH)2] is a spectral mixture of Cu and Co but optically separated by Co2+ and Cu2+ peaks at 8385 and 7520cm−1. Vibrational spectra of carbonates show a number of bands in the 7000–4000cm−1 region attributable to overtones, combination of OH stretching and deformation modes. They appear to be uniform in nature since the structure of rosasite group minerals is identical. The complexity of these features varies between samples because of the variation in composition and hence is useful for discriminating different hydrous carbonates. [Copyright &y& Elsevier]

Abstract: Hydrotalcite-like compounds of the formula Ni x Zn6−x Al2(OH)16(SO4)·4H2O where x varies from 0 to 6, equivalent to a zinc-substituted carrboydite have been synthesised and characterised by X-ray diffraction, electron microscopy and vibrational spectroscopy. Both the d (003) spacing and the crystallite size are a function of the amount of zinc replacement for nickel in the carrboydite-like compounds. Transmission electron microscopy (TEM) shows the clay-like crystal structure for these hydrotalcite compounds. These compounds were characterised by vibrational spectroscopic techniques and a comparison made with the naturally occurring minerals. Additional bands in the sulphate antisymmetric stretching and bending region leads to the conclusion that the symmetry of the sulphate anion is reduced inferring the bonding of the sulphate anion to the hydrotalcite hydroxyl surface. [Copyright &y& Elsevier]

Abstract: Raman spectra at 298 and 77K of three uranophane samples from different localities are described and interpreted. The spectra are sample dependent. U–O bond lengths in uranyls are calculated from the spectra and compared with the published data of single crystal structure and EXAFS spectroscopy. Hydrogen-bonding of water molecules and silanols is discussed and the ‘proton mobility’ in uranophane sheet crystal structure is assumed. [Copyright &y& Elsevier]

Thermogravimetry combined with mass spectrometry has been used to study the thermal decomposition of a synthetic hydronium jarosite. Five mass loss steps are observed at 262, 294, 385, 557 and 619°C. The mass loss step at 557°C is sharp and marks a sharp loss of sulphate as SO3 from the hydronium jarosite. Mass spectrometry through evolved gases confirms the first three mass loss steps to dehydroxylation, the fourth to a mass loss of the hydrated proton and a sulphate and the final step to the loss of the remaining sulphate. Changes in the molecular structure of the hydronium jarosite were followed by infrared emission spectroscopy. This technique allows the infrared spectrum at the elevated temperatures to be obtained. Infrared emission spectroscopy confirms the dehydroxylation has taken place by 400 and the sulphate loss by 650°C. Jarosites are a group of minerals formed in evaporite deposits and form a component of the efflorescence. The minerals can function as cation and heavy metal collectors. Hydronium jarosite has the potential to act as a cation collector by the replacement of the proton with a heavy metal cation. [ABSTRACT FROM AUTHOR]