Nanograin formation and reaction-induced fracturing due to decarbonation: Implications for the microstructures of fault mirrors

- Heating dolomite and calcite to T≥600 °C creates a pervasive nanogranular coating.
- When wetted heat-formed nanograins are unstable but those in fault mirrors are stable.
- Star-shaped cracks are found in dolomite and calcite heated to T≥600 °C.
- This is related to volume decrease due to decarbonation initiating at defects.
- Mechanical stresses due to decarbonation may contribute to grain size reduction.