## 3 Results and Discussion  
### The Determination of Mineralogical Composition  
The whole-rock thin section and the photomicrographs (Figure 5a-f) show the characteristics of a micaceous sandstone [46; 47; 48]. The quartz arenite rock is characterized by a poorly sorted grain distribution, predominantly composed of angular to subrounded grains of quartz (>90%), with clastic flakes of muscovite (5-10%) and up to a 5% composition of feldspars (Figure 5). The matrix, comprising 5-10% of the rock, consists of authigenic clay minerals, suggesting an immature texture of the rock. The muscovite flakes are often distorted and bent between the clastic grains, suggesting compaction (Figure 5b,f). The quartz arenite samples from the church show elongated muscovite grains within monocrystalline quartz grains (Figure 5e,f), suggesting an initial sedimentary environment with muscovite flakes as detrital grains. During diagenesis, silica-rich fluids precipitated quartz crystals around the detrital muscovite grains, embedding them within the quartz matrix. The elongated shape suggests compaction during burial and diagenesis. RS analyses have revealed the presence of quartz (SiO\({}_{2}\)) and muscovite [KAl\({}_{2}\)(AlSi\({}_{3}\)O\({}_{10}\)) (OH)2] in the sample, confirming the mineral composition observed in the thin sections. The Raman spectrum of the sample has the strong characteristic Raman peak of quartz located at 467 cm\({}^{-1}\), which is attributed to the \(\
u_{1}\) symmetric stretching of Si-O-Si [49]. The peaks at 412 cm\({}^{-1}\) and 1087 cm\({}^{-1}\) can be assigned to muscovite. Figure 6 shows the recorded Raman spectrum of the sample of the present study compared with the reference RS of quartz (R150091) and muscovite (R150091) from the RRUFF database. XRD is a suitable method for investigating crystalline phases contained in various rocks. The structural analysis of the investigated sample was also corroborated with the other applied experimental methods. The powder X-ray pattern is presented in Figure 7 and highlights the presence of four minerals. Silicon oxide found in the form of quartz, SiO\({}_{2}\) (PDF 00-087-2096), is the dominant mineral, highlighted by the intense peak that appears at 20 = 26.6\({}^{\circ}\) and a series of smaller peaks that appear at high diffraction angles. Another two present phases are muscovite and illite, with the latter acting as a cohesion agent of the muscovite crystals, both being identified by the specific diffraction peak at 20 = 8.80\({}^{\circ}\) and other peaks seen at 17.5\({}^{\circ}\) and 26.8\({}^{\circ}\). Kaolinite represents another constituent phase whose presence is indicated by the slightly broader diffraction peaks compared with the rest of the phases and appears at 20 = 12.21\({}^{\circ}\), 21.0\({}^{\circ}\), and 24.8\({}^{\circ}\). We can conclude that by using XRD, the quartz and muscovite were both confirmed (Figure 7). Moreover, the clay matrix comprises kaolinite and some illite, both of which were identified only with XRD analysis (Figure 7). Sandstone, like other sedimentary rocks, is susceptible to biodeterioration due to microbial activity. Over time, depending especially on the climate conditions, fungal colonization and activity can contribute to the degradation of sandstone, resulting in changes in time to its texture, color, and mechanical properties [50]. Figure 5: (**a,d,e**) Photomicrographs of quartz arenite samples under cross-polarizers; (**b,c,f**) circular cross-polarizers. Abbreviations: m-Qz = monocrystalline quartz; p-Qz = polycrystalline quartz; Ms = muscovite; Pl = plagioclase; Fsp = feldspar; p.s. = pore space; m = clay matrix; * = muscovite crystals embedded in quartz. Scale bars on the photomicrographs are 100 \(\upmu\)m.  
Figure 6: Recorded Raman spectrum of the sample of the present study compared with the reference RS of quartz (R150091) and muscovite (R150091) from the RRUFF database [51].