The lettering in Figure 3 shows some of the different spectral features of this mineral. The bands labelled A show the hydroxyl stretching bands of the hectorite which are retained to quite high temperatures. B shows organic impurities in the mineral. C demarks the presence of carbonates in the mineral. D is the SiO stretching bands of the hectorite.
E is the hydroxyl deformation vibration corresponding with the hydroxyl stretching bands at A .
The infrared absorption spectra of the hectorites are identical to the emission spectra. These spectra enable the molecular structure of the hectorite to be obtained. Infrared absorption and emission spectra of a standard and an unknown hectorite One of the obvious advantages of infrared emission spectra is the ability to obtain a suite of temperature-consecutive spectra of a sample in situ at the elevated temperatures. Figure 4 clearly shows such a suite, exemplified by a pillared hectorite. The pillar is fixed in the layers by thermal treatment at around 600 C where the Al 13 is transformed into Al 2 O 3 .