Thermal expansion behavior of igneous rocks

New experimental data on the thermal expansion of several igneous rocks over the range 25–550°C show that the observed thermal expansion is a function of crack porosity, heating rate, and previous maximum temperature as well as mineralogical composition and preferred crystal orientation. For heating rates if≤2°C/min and a maximum temperature ≤250°C; expansion curves are reproducible, may show a small hysteresis but no permanent strain, and the coefficient of thermal expansion (α) is approximately that calculated from the single crystal values of the constituent minerals. For highly cracked rocks α is significantly less than the calculated value. For heating rates >2°C/min or T > 35°C, new cracks and hence permanent strain are produced in the sample and α is systematically decreased. Recycling to the same temperature produces additional cracks until a steady state is reached after 2–5 cycles.