Eighteen soil samples were collected from the subsequent layers of nine soil profiles representing the calcareous soils of El–Arish and Ras Sudr. Field evidence showed the different forms of soil carbonates, crust, concretions, nodules and soft powdery (diffused). The collected soil samples were analysed to determine some of their physical and chemical characteristics, then X-rayed to determine the crystalline soil carbonate minerals.                 The obtained results showed that total soil carbonates varies widely from 2.98 to 50.21% and 32.49 to 59.85% in El-Arish and Ras Sudr soils, respectively. The depthwise distribution of carbonates follows nearly two patterns characterized by a tendency of increase and irregular distribution down- ward the soil profiles with no distinctive formation of pedogenic calcic horizon.                 The carbonate mineralogy revealed the dominance of calcite, ankerite and monohydrocalcite in both soils with slight occurrence of other eleven crystalline carbonate minerals, of which gaudefroyite was identified in both soils forming about 4-6% of carbonate minerals. Minrecordite, dolomite and northupite were also indentified in traceable amounts (average 4.09 and 4.80% of soil carbonate), while other minerals constitute an average weighted means in soil profiles, not exceeding 4% of carbonates for each mineral.                 The results of carbonate mineralogy were interpreted in light of soil origin, genesis and formation which clarified that most carbonate minerals are geogenic or lithogenic, derived from the limestone- enriched rocks of El–Tih and Egma plateau. But this does not deny the authogenic or pedogenic orgin of some carbonates due to weathering and chemiprecipitation enhanced by the increasing concentrations of soluble Ca⁺⁺, Mg⁺⁺ and HCO₃ions and CO₂ from biotic origin as well as the links between abiotic and biotic CaCO₃ whose interactions are also discussed. However, the biogeochemical interaction is seemingly slow, weak and needs long time to reach distinguishable calcic horizon under the prevailing arid environment.