instrumental techniques applied to mineralogy and geochemistry

Raman, Conventional Infrared and Synchrotron Infrared Spectroscopy in Mineralogy
and Geochemistry: Basics and Applications
75
FIGURE 8. Raman scattering and ATR IR spectra of CO 2 -laser-treated human dental enamel
(consisting mainly of hydroxyapatite, 12% water and 3% organics). After Klocke et al., 2006.
In the IR spectra from inside the laser spot of the samples treated in super pulse laser
mode (E(1|5|p, curve c) the second order P-O absorption peaks are poorly resolved,
which gives further evidence for a lowering of the degree of crystallinity, confirming the
Raman results. The smearing of the C-H stretching bands around 2900 cm -1 (IR)
indicates an impact of the laser treatment on the organics. Increased intensity of the IR
band at 3750 cm -1 (surface OH groups) is a sign of grain size reduction under irradiation.
Silicates: Silicates are mineralogically and geochemically very important as well
crystallographically very exciting class of minerals. In their complex mineral structures,
“molecular groups” are not always readily identifiable, especially where the structure is
strongly bonded in two or three dimensions. An isolated SiO 4 group (or any tetrahedral
XY 4 group) would have nine internal degrees of freedom but only four modes of
vibration due to degeneracy (Fig. 9). In structures with isolated SiO 4 tetrahedra it is a
very useful starting point to
consider the vibrational modes of
FIGURE 9. Normal modes of vibration of tetrahedral
molecules and vibrational frequencies of isolated
SiO 4 tetrahedra (Nakamoto, 1997).
SiO 4 tetrahedron. The SiO 4
stretching modes are in the high
frequency range: n 1 symmetric and
n 3 asymmetric stretch ~800-1100