The Fourier-transform infrared (FTIR) spectra showed consistent absorption bands across the studied soil profiles, reflecting both mineralogical and organic components. The band at 1630–1650 cm⁻¹ was attributed to carboxylic functional groups, indicating the presence of oxidized organic compounds. Strong absorptions in the 1100–1000 cm⁻¹ region were assigned to Si–O stretching vibrations, characteristic of silicate minerals, particularly quartz and clay minerals, with overlapping contributions from C–O stretching associated with polysaccharides and ester groups. An additional band at 1396 cm⁻¹ was related to carboxylate groups, likely reflecting organic matter complexation with Al³⁺. Minor variations in band intensities among profiles suggest differences in organic matter content and mineral–organic associations, supporting contrasting soil formation processes and varying degrees of organic matter stabilization in soils from Catimbau National Park