<p>This study investigates Algerian loess, a representative example of desert loess in North Africa, with a focus on its implications for construction engineering. Due to their high water sensitivity, loess soils pose significant geotechnical challenges. A thorough understanding of their geotechnical and mechanical properties is essential for geologists and engineers involved in designing and constructing on such soils. This research contributes to the scientific database on loess from the Ghardaïa region by conducting comprehensive analyses, including grain-size analysis; chemical and mineralogical characterization; direct shear, compaction, and rheology; and thixotropy assessment via hysteresis-loop evaluation, which is critical for predicting long-term structural stability. The physical results reveal a coarse texture, indicating silty loess at the Daïa Ben Dahoua site and sandy loess at the Metlili site. Chemically, the Ghardaïa loess is alkaline and saline, predominantly composed of silica and calcite, with minor amounts of kaolinite, montmorillonite, iron, and aluminium oxides. The mechanical testing indicates low cohesion and yield stress, and high internal friction angles, reflecting a loose granular structure weakly cemented by carbonate–saline bonds. Rheological testing results suggest that the samples exhibit non-Newtonian, shear-thinning, and thixotropic behavior, with viscosity strongly dependent on solid concentration. This study provided links between surface texture, mineralogy, and cementation to mechanical and rheological behavior, which were used to identify key microstructural mechanisms. This, in turn, contributes to the instability of loess, including weak interparticle bonding, limited clay-mediated cohesion, and carbonate bridges that are sensitive to moisture. This information represents a significant resource for application in construction-related engineering fields, including foundations, earthworks, hydraulic structures, and building materials.</p>