## 3 Experimental Results
### Microscopic Weathering Indicators  
#### 3.2.1 Variation of Composition Change Law  
Figure 12 illustrates variation curves depicting the relative content of different components in two types of rocks obtained from X-ray diffraction analysis. To quantitatively analyze the changes in the composition content of rock samples after different numbers of cycle, a table (Table 3) was created to present the composition content of sandstone samples after 0, 5, 15, and 25 cycles. As shown in Figure 11a, as the number of cycles increased, the calcite content in the limestone samples consistently decreased while the dolomite content gradually increased. Notably, the peak value of dolomite continued to rise towards the conclusion of the experiment. This phenomenon can be attributed to the higher lattice energy and crystal stability of dolomite compared to calcite. Additionally, dolomite exhibits stronger ionic bonds and better resistance to weathering. Consequently, under similar environmental conditions, dolomite is less susceptible to disintegration [29]. Figure 11b primarily showcases variations in the composition and contents of sandstone samples.  
Figure 11: Sandstone and limestone uniaxial compressive strength and loss variation curves. (**a**) Two types of rock uniaxial compressive strength variation curves; (**b**) two types of rock strength loss variation curves.  
The curve in the figure indicates that the quartz content is the highest and continues to increase as the number of cycles increases. Following quartz, feldspar minerals exhibit the second-highest content. By the 25 th cycle, the distribution range of feldspar minerals was markedly different and narrower, with only a few small peaks remaining. Notably, the variation in calcite content is the smallest when compared to other substances [30]. This indicates that the test methods and ranges of different precision instruments should be clarified when measuring the micro-weathering indexes of rocks, and errors caused by experimental tests should not be ignored.  
To quantitatively analyze the changes in the composition content of sandstone rock samples at different cycle times, a table (Table 3) was produced from the performed X-ray analysis to present the composition of sandstone samples after 0, 5, 15, and 25 cycles. The total content of feldspar minerals and calcite decreased from 40-48% to 24-35%. This decrease can be attributed to the hydrolysis and hydration of these substances, with the intensity of the reaction increasing with longer immersion times. Additionally, the rock samples naturally contain clay minerals, and some minerals undergo illitization or kaolinitization, resulting in a 5-10% increase in clay mineral content. In comparison to other components, the quartz content continues to increase and represents over two-thirds of the total content by cycle 25. Based on the aforementioned analysis, it is evident that the limestone samples primarily consist of dolomite and calcite, and alterations to these two substances primarily occur during the salt weathering process. Specifically, after 25 cycles of salt weathering, the relative content of dolomite in the limestone samples increased from 25-35% to 55-65%, whereas the relative content of calcite decreased from 58-70% to 32-45%.