## 4 Physical and Mechanical Parameters  
### Porosity  
Figure 2a shows the changes in porosity with temperature. At room temperature, granite exhibits low porosity, indicating minimal visibility of the original pores and fissures. Overall, as the temperature rises, granite porosity increases. This is attributed to the formation of thermal microcracks. However, a slight decrease in porosity was observed, mostly at the beginning of the heat treatment, suggesting mineral grain expansion. Below 100 \({}^{\circ}\)C, the loose bonding of rock minerals allows water trapped in tiny pores and between layers to escape. Simultaneously, heat treatment prompts mineral particles to expand, leading to the closure of primary cracks. Consequently, rock porosity slightly decreases. Within the 100-300 \({}^{\circ}\)C range, physically combined water within the rock evaporates, exerting pressure that facilitates the expansion of cracks and pores. Notably, differences in thermal expansion between feldspar and quartz become apparent, leading to uncoordinated thermal expansion and crack initiation. In the 300-600 \({}^{\circ}\)C range, nearly all trapped and physically combined water evaporates, while chemically bound water dissociates, disrupting the mineral lattice. As a result, erratic trends in porosity are observed within the 300-600 \({}^{\circ}\)C \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{2}{c}{**Temperature (\({}^{\circ}\)C)**} & \multicolumn{3}{c}{**The Neighboring Minerals**} \\ \cline{2-4}  & **Quartz and Quartz** & **Quartz and Biotite** & **Quartz and Feldspar** & **Biotite and Feldspar** \\ \hline
25 & \multicolumn{3}{c}{No intergranular cracks in the mineral boundaries} \\
200 & Crack initiation & No crack initiation & Crack initiation & No crack initiation \\  & The intergranular & No intergranular & The intergranular & The intergranular \\
400 & cracks occur between & cracks in the & cracks occur between & cracks occur between \\  & two quartz minerals & mineral boundaries & quartz and & biotite and \\  & & & feldspar minerals & feldspar minerals \\  & Widening of the & The intergranular & Widening of the & Widening of the \\
600 & intergranular cracks & cracks occur between & intergranular cracks & intergranular cracks \\  & in quartz minerals & quartz and & between quartz and & between biotite and \\  & & biotite minerals & feldspar minerals & feldspar minerals \\
800 & \multicolumn{3}{c}{Intergranular cracks fully developed with large apertures.} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The development of intergranular cracks due to temperature. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{2}{c}{**Temperature**} & \multicolumn{3}{c}{**Mineral**} \\ \cline{2-4}
**(\({}^{\circ}\)C)** & **Quartz** & **Feldspar** & **Biotite** \\ \hline
200 & \multicolumn{3}{c}{No intragranular cracks} \\  & Intragranular cracks are & Intragranular cracks are & \\
400 & initiated in large quartz & initiated in & Almost intact \\  & minerals (crystals \textgreater{} 0.5 mm) & feldspar minerals & Initiation of intragranular cracks \\
600 & Widening of the intragranular & Widening of intragranular & in large weak biotite minerals \\  & cracks in quartz minerals & cracks in feldspar grains & (parallel to the grain boundaries \\
800 & \multicolumn{3}{c}{Macroscopic intragranular cracks with large apertures} \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The development of intragranular cracks due to temperature. temperature range, as shown in Figure 2a. This temperature range may correspond to a transition zone. Despite the continued thermal expansion of mineral particles and the initiation of new cracks, some cracks and pores may close due to particle expansion, resulting in little to no increase in porosity. Overall, porosity exhibits only slight growth up to 600 \({}^{\circ}\)C, implying minor structural changes due to existing and new microcrack development.