Mineralogical and Geochemical Baseline Characterization using FTIR and Raman Spectroscopy of Urban Soils: A case Study from Vasai–Virar City Municipal Corporation, Maharashtra, India

Urban soils integrate pedogenic, lithogenic, and anthropogenic material in proportions that are rarely characterized despite their growing relevance to urban ecosystem services, including carbon storage. This study presents a mineralogical baseline for twenty surface soil samples collected across the Vasai–Virar City Municipal Corporation (VVCMC), Maharashtra, using attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) and 785 nm Raman spectroscopy. The study shows Kaolinite and quartz were the dominant phases identified by FTIR. With a well-resolved kaolinite OH-stretching doublet (~3695/3620 cm⁻¹) present in six of twenty samples and a residual quartz Si–O–Si bending doublet (~790/685 cm⁻¹) recurring across the samples. Raman spectroscopy independently confirmed anatase (TiO₂) in nine samples and quartz in one. While a further nine samples returned no confident identification, predominantly due to CCD etalon fringing and fluorescence rather than an absence of Raman-active phases. A calcite doublet (~1415–1450/873–874 cm⁻¹) appeared in three samples. Therefore, the assemblage of dominant kaolinite, residual quartz, and accessory anatase, with no detectable feldspar or mica. It is consistent with an advanced-stage, kaolinite–quartz lateritic (ferralitic) soil derived from in situ weathering of the Deccan Trap basaltic hinterland. The use of FTIR and Raman spectroscopy proved valuable both for direct phase confirmation and for diagnosing instrument-specific data-quality limitations.