## 3 Results and Discussion
### Identification of Minerals through FTIR Analysis  
The FTIR spectra of the studied brick samples are depicted in Figure 4a. Since a few FTIR spectra are not easy to interpret on a whole-range scale, the graphs were separated into two ranges spanning 1200-400 cm\({}^{-1}\) and 4000-3000 cm\({}^{-1}\) (Figure 4b,c). The minerals identified in the spectra were based on existing literature sources (listed in Table 1). They include quartz, feldspar (albite, orthoclase), kaolinite, palygorskite, chlorite, organic carbon, cerussite, hematite, and magnetite. All the brick samples under investigation contain quartz, kaolinite, organic carbon, and palygorskite (barring Rukmini Garh). The presence of quartz was confirmed by characteristic vibrational peaks at 457-458 cm\({}^{-1}\) (Si-O asymmetrical bending), 460-463 cm\({}^{-1}\) (Si-O asymmetrical bending), 692-693 cm\({}^{-1}\) (Si-O symmetrical bending), and 776-778 and 795 cm\({}^{-1}\) (Si-O symmetrical stretching). The existence of quartz in the Mouramora-1, Pratima Garh, and Rukmini Garh brick samples was supported by the presence of weak absorption peaks at 1619 cm\({}^{-1}\) and 1870-1876 cm\({}^{-1}\). The feldspar group of minerals is merely present in the Pratima Garh brick sample, which included orthoclase, microcline (K-feldspar), and albite (Na-feldspar). Their presence was established by identifying the vibrational peaks at 1050 cm\({}^{-1}\) (Si-Al-O stretching for microcline feldspar), 642 cm\({}^{-1}\) (Al-O coordination vibrations suggesting orthoclase feldspar), and 725 cm\({}^{-1}\) (Al-O-Si stretching for albite feldspar). In general, four significant IR spectra of OH-stretching regions are employed to distinguish kaolinite, with relative intensities of 3695, 3665, 3650, and 3620 cm\({}^{-1}\)[40; 41]. However, the presence of other minerals may influence the intensity and resolution of  
Figure 4: FTIR spectrum of studied brick samples: (**a**) FTIR spectrum ranges from 4000–400 cm\({}^{-1}\), (**b**) FTIR spectrum ranges from 4000–3000 cm\({}^{-1}\), and (**c**) FTIR spectrum ranges from 1200–400 cm\({}^{-1}\) (Q—Quartz, Or—Orthoclase, A—Albite, Mt—Magnetite, Hm—Hematite, K—Kaolinite, Plg—Palygorskite, C—Carbonates, Ch—Chlorite, OC—Organic Carbon). these vibration bands. The studied samples encompass no prominent kaolinite peaks at the expected values. In Ref. [41] the authors assigned the OH stretching region peak with an intensity of 3647 cm\({}^{-1}\) as kaolinite. Under this assumption, the presence of this peak with weak OH stretching of the inner hydroxyl group in the Mouramora-2 and Pratimagarh samples confirms the signatures of kaolinite. The spectra region from 3671 to 3851 cm\({}^{-1}\) represents the OH stretching of water molecules. The 3460-3496 cm\({}^{-1}\) spectra imply mixed layered OH stretching and bending vibrations of inner-surface hydroxyl groups. The OH stretching of the inner hydroxyl group chlorite mineral was also observed in the Mouramora-2 samples at 3565 cm\({}^{-1}\). The IR spectrum for kaolinite with thin particles exhibits peaks at 1105 and 695 cm\({}^{-1}\); however, as the particle size increases, the vibrational bands shift to 1080 and 689 cm\({}^{-1}\)[40]. Barring the sample Padumpukhuri, the other samples display broadening bands at 1080 and 1084 cm\({}^{-1}\). Carbonate minerals have been found in three different samples: Mouramora-3, Padum Pukhuri, and Rukmini Garh, with FTIR peaks at 1381, 1384, and 1788 cm\({}^{-1}\). The mineral with a prominent relative intensity at 1396 cm\({}^{-1}\) was identified as cerussite [42]. However, [PERSON] et al. [28] also considered the peaks at 1380-1385 cm\({}^{-1}\) as indicative of cerussite. Hence, the presence of spectra at 1381, 1384, and 1788 cm\({}^{-1}\) is in good agreement with the carbonate minerals cerussite and calcite, respectively. The complex nature of absorption bands in stretching and bending regions of water molecules is characteristic of palygorskite. Palygorskite may be responsible for the presence of bands in the region of 1623-1630 cm\({}^{-1}\).