The quartz-cristobalite transformation in heated chert rock composed of micro and crypto-quartz by micro-raman and FT-IR spectroscopy methods

The quartz-cristobalite transformation in heated natural chert (flint) rock composed of micro- and crypto-quartz was investigated in the temperature interval of 1000-1300°C by micro-Raman spectroscopy, FT-IR spectroscopy, X-ray diffraction and Scanning Electron Microscopy. A small amount of crystobalite was first observed in the chert after heating at 1000°C for 1 h and the transformation was almost completed after heating at 1300°C for 24 h. On the other hand, cristobalite was not detected in well-crystallized pure quartz after heating under the same conditions. The transformation occurs as a solid state nucleation and crystal growth of cristobalite replacing quartz at high-temperatures. The chert rock is naturally rich in crystal defects and boundaries which serve as nucleation sites and enable an earlier quartz-cristobalite transformation.