Thermal Decomposition of Silicate Minerals

NMR spectroscopy, especially Si NMR, has proved to be a valuable technique for studying thermal decomposition of minerals, especially in cases where the intermediate phases are poorly crystalline or X-ray amorphous. 

The reactions of several other minerals which thermally decompose to form mullite have been studied by Si and Al NMR. These include the mica mineral muscovite, which also contained sufficient iron to permit a complementary Fe Mossbauer study (MacKenzie et al. 1987), the hydroxyfluoride mineral topaz (Day et al. 1995) and the semi-amorphous aluminosilicate minerals allophane (MacKenzie et al. 1991) and imogolite (MacKenzie et al. 1989). The same combination of NMR nuclei has been used to study the thermal decomposition of other aluminosilicates including an illite-rich clay (Roch et al. 1998), montmorillonite (Brown et al. 1987), and a related mineral, Fuller s Earth (Drachman et al. 1997). NMR has also been used to study the effect of water vapour on the thermal decomposition of montmorillonite clay compacts (Temuujin et al. 2000a). 

Studied by and NMR include talc (MacKenzie and Meinhold 1994b) and synthetic hectorite (Mandair et al. 1990, MacKenzie and Meinhold 1994c). 

If all these results are combined in a single plot, the resulting line is 

However, the scatter in this simple generalised relationship, especially for the chain silicates, reduces its usefulness, and indicates that other factors such as next-nearest-neighbour interactions are playing an important role in determining the chemical shift. 

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