instrumental techniques applied to mineralogy and geochemistry

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Raman, Conventional Infrared and Synchrotron Infrared Spectroscopy in Mineralogy and Geochemistry: Basics and Applications 73 Large number of overlapping spots was analyzed in a confocal geometry using apertures of 4 or 6 m and a step size of 2 m in a grid pattern accessed by an automated stage. The brilliant synchrotron IR light of ANKA is providing the required high spatial resolution. The results show that for all three types of defects in the olivine matrix, i.e. cracks, grain boundaries and Cr-spinel inclusions, the water content increases systematically by a factor of 5–10 towards the defect. Similarly, the defects are all surrounded by halos of water, which increases towards the defects. The data are used to derive passage of aqueous fluids through the lithosphere thus obtaining more detailed information about the ascent rates of kimberlitic melts and their potential for diamond deposits. Step-by-step mapping in a confocal arrangement, as shown in the previous example, provides the best spatial resolution and image contrast. The severely reduced flux on the detector at sampling size approaching (or even smaller) than the diffraction limit can be compensated by the high brilliance of the SR-IR. One disadvantage that remains is the FIGURE 7. IR images of a CO 2 -H 2 O FI with the corresponding H 2 O and CO 2 long time required to scan the sample (e.g. the spectra as extracted from a single pixel sample area shown in the map in Fig. 6, right, of the FPA. was scanned in ~10 h). Much faster one-shot images can be acquired using a multielement focal plane array (FPA) detector. One such study carried out at ANKA involved imaging with a 64 x 64 pixel FPA detector (Fig. 7, Moss et al., 2008). Each pixel in these images corresponds nominally to 1.15 m 2 on the sample. The time for this experiment was less than 5 minutes! ANKA was the first to demonstrate the value of such multielement detectors at synchrotron IR beamlines (Moss et al., 2006), and this work has proved highly influential, leading to many beamlines worldwide acquiring such detectors. One should keep in mind that this is an apertureless technique and the true spatial resolution as well as the image contrast are deteriorated by diffraction and scattering.
74 Biliana Gasharova Structural studies: biominerals Structural changes and dehydration of water/OH containing (bio)minerals could be monitored usually very well by vibrational spectroscopy. In a study by Klocke et al. (2006) thick sections of extracted human teeth were irradiated by CO 2 -laser to simulate teeth treatment under different laser operational modes. Raman and IR microspectroscopy were the methods of choice, since the aim was to analyze the gradient of structural alteration and molecular exchange across the CO 2 -laser irradiated areas in the dental enamel. The IR absorption spectra were measured with an IR microscope equipped with Ge-ATR objective, for the samples were too thick to observe first-order phonons in transmission geometry. The IR spectra in Fig. 8 indicate loss of water (broad stretching band at 3232 cm -1 and the bending band at 1649 cm -1 ) and OH (sharp peak at 3570 cm -1 ) as a function of distance from the center of the CO 2 -laser spot after irradiation of human dental enamel (outside (curves a), at the periphery (curves b) and inside (curves c) the laser spot. The IR spectra in Fig. 8 show as a function of distance from the center of the CO 2 -laser spot a decomposition of CO 3 groups present in the apatite structure (bands around 1400-1550 cm -1 ), their consequent transformation into CO 2 groups (bands at 2343 cm -1 ) and their final disappearance in the center of the laser spot. For samples E(1|5|c), those irradiated in a CW laser mode, the CO 3 -CO 2 conversion is accompanied by rearrangement of the CO 3 groups in the apatite crystal structure. As the IR absorption at 1412 and 1547 cm -1 is associated with CO 3 groups substituting for PO 4 (so-called B-type CO 3 ) and for OH (A-type CO 3 ), resp., the observed change in the relative intensities represents a relative decrease of the amount of B-type and an increase of the amount of A-type CO 3 groups. Comparison between the structural changes in the enamel apatite observed in this study to those in heated samples revealed that under laser treatment the achieved average temperature in the center and near the CO 2 -laser crater was about 1100 and 700 K, resp. The most intense Raman peak at ~963 cm -1 arises from the symmetric stretching mode of PO 4 groups. Its broadening and the appearance of many additional shoulders after irradiation indicates, e.g. variations in the P-O bond lengths and it is evident for structural amorphization.
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