Non-dislocation thermal etch pits on calcite cleavages

Thermal etch pits with rhombic outlines on the cleavage surfaces of natural calcite crystals are observed in a narrow range of etching temperature between 540 and 625 °C in air. The thermal etch rates V_t and V_s of the tangential dissolution of ledges and the surface dissolution respectively were determined in the above temperature range. The activation energies E_{t th} and E_{s th} of tangential thermal dissolution and surface thermal dissolution respectively are calculated and are compared with those of controlled chemical dissolution initiated to produce dislocation etch pits on calcite cleavages. A quantitative study of the activation energies suggests that the thermal etch pits on calcite cleavage faces originate at dislocation-free sites such as kinks, steps and/or impurity centres.