<p>This study investigates the fracture behavior of limestone samples subjected to varying thermal treatment conditions, including different peak temperatures and heating rates. The experimental process evaluated the mechanical response of the rocks by analyzing the correlation between Crack Mouth Opening Displacement (CMOD) and applied load. The results demonstrate that thermal exposure significantly alters the fracture toughness (KIC) and crack propagation behavior. Higher temperatures and faster heating rates were found to accelerate crack initiation and propagation due to induced thermal stresses and microstructural degradation. Mineralogical composition and petrographic characteristics, particularly grain size and porosity, strongly influenced thermal sensitivity. The findings indicate that crack propagation is significantly more rapid in the fine-grained limestone with some coarse calcite (M1) than in the small-grained, amorphous calcite and quartz limestone (L1). This behavior strongly depends on both the heating rate and the peak temperature. This indicates that thermally induced damage is largely dependent on the intrinsic properties of the rock, which must be considered in engineering applications involving high-temperature exposure or thermal fatigue.</p>