Abstract: The montmorillonite in Heping, Guangdong province was studied by chemical analysis, DTA, TG, XRD, IR, AFM and MAS NMR. It is
found that when the temperature is between 500～700℃, The Si and Al spectra of montmorillonite display the spectrum characteristic
of meta-montmorillonite. When the thermal treatment temperature reaches 659℃, the hydroxyl in octahedra sheet begins dehydrating, but the
layer structure is maintaining, this process is corresponding to Al(Ⅵ) turning to Al(Ⅳ) in octahedra sheet. When the temperature reaches 900℃, the Si spectra relevant to montmorillonite disappear, that
means the layer structure of montmorillonite is destroyed, and the new mineral phase χ-SiO₂ is found. When the temperature reaches 1000℃,
there is more χ-SiO₂ phase produced by phase change, meanwhile the Al spectra of thermal products change greatly. When the temperature reaches
1200℃, cristobalite and mullite phases appear. When the temperature reaches 1350℃, the cristobalite and mullite phases reduce a few, and more
cordierite phases appear.

Key words: montmorillonite, thermal treatment, MAS NMR, cordierite