Raman spectroscopy of basic copper(II) and some complex copper(II) sulfate minerals: Implications for hydrogen bonding
The minerals used in this study were, Langite (sample D4379, Cornwall, U.K.), Brochantite (samples D20320 Chuquicamata, Chile and D28957 Bisbee, Arizona, U.S.A.), Antlerite (M33489 Antlerite, Chuquicamata, Chile), Posnjakite (M27302 Drakewalls adit, near Gunnislake, Cornwall, U.K.), Cyanotrichite (G14601 Maid of Sunshine Mine, Cochise County, Arizona, U.S.A.), Devilline (G17182 Spania Dolina, Czechoslovakia), Ktenasite (G24983 Glomsevo Kollen, Amot Modum, Norway), Serpierite (G4034 Laurium, Greece), Glaucocerinite (G17641 Maid of Sunshine Mine, Cochise County, Arizona, U.S.A.). The identity of each phase was confirmed using x-ray diffraction, and the compositions checked using EDX measurements. The crystals of the minerals were placed and oriented on a polished metal surface on the stage of an Olympus BHSM microscope, which is equipped with 10× and 50× objectives. The crystals were oriented to provide maximum intensity. All crystal orientations were used to obtain the spectra. Power at the sample was measured as 1 mW. The incident radiation was scrambled to avoid polarization effects. The microscope is part of a Renishaw 1000 Raman microscope system, which also includes a monochromator, a filter system, and a Charge Coupled Device (CCD). Raman spectra were excited by a Spectra-Physics model 127 He-Ne laser (633 nm) at a nominal resolution of 4 cm−1 in the range between 100 and 4000 cm−1. Repeated acquisitions using the highest magnification were accumulated to improve the signal to noise ratio in the spectra. Spectra were calibrated using the 520.5 cm−1 line of a silicon wafer. Spectroscopic manipulation such as baseline adjustment, smoothing and normalization were performed using the Spectracalc software package GRAMS (Galactic Industries Corporation, NH, USA). Band component analysis was undertaken using the Jandel “Peakfit” software package, which enabled the type of fitting function to be selected and allows specific parameters to be fixed or varied accordingly. Band fitting was done using a Gauss-Lorentz cross-product function with the minimum number of component bands used for the fitting process. The Gauss-Lorentz ratio was maintained at values greater than 0.7, and fitting was undertaken until reproducible results were obtained with squared correlations, r2, greater than 0.995.
Figure 1 shows Raman spectrum of the hydroxyl-stretching region of (a) antlerite, (b) brochiantite, (c) posnjakite, (d) langite, and (e) wroewolfeite. Figure 2 shows Raman spectrum of the hydroxyl-stretching region of (a) cyanotrichite, (b) devilline, (c) glaucocerinite, (d) serpierite, and (e) ktenasite. Figure 3 shows Raman spectrum of the hydroxyl-stretching region of (a) cyanotrichite, (b) devilline, (c) glaucocerinite, (d) serpierite, and (e) ktenasite. Figure 4 is the hydrogen-bond distance as a function of the peak position of the symmetric SO4-stretching vibration. Figure 5 shows Raman spectrum of the SO4 bending region of (a) antlerite, (b) brochiantite, (c) posnjakite, (d) langite, and (e) wroewolfeite. Figure 6 shows Raman spectrum of the low wavenumber region of (a) cyanotrichite, (b) devilline, (c) glaucocerinite, (d) serpierite, and (e) ktenasite.