This chapter aims to characterize the mineralogical composition of lagoonal sediments of the Oualidia lagoon. In this context, one sediment core and three surface sediments were collected from the lagoon and analyzed to determine their mineralogical composition and particle size using the X-ray Diffraction (XRD) technique and a laser diffraction particle size analyzer, respectively. The mineralogical and chemical composition profiles indicate that the sediment core is entirely under marine influence. In contrast, the study of the spatial distribution of surface sediments reveals that the lagoon is currently more open to continental conditions. The statistical analysis of the data revealed three geochemical and mineralogical associations in the sediment core, highlighting the complex interaction between detrital, biogenic, and evaporitic processes within the sedimentary system of the Oualidia lagoon. The findings provide a framework for understanding the lagoon’s recent geochemical and mineralogical evolution over the past 40 years, with implications for sediment dynamics, coastal management, and the potential impacts of human activities.