Twenty five soil samples were collected from various parts of uncultivated areas in Iraq including Rabe'a, Mosul, Hatra, Beygee, Balad, Radhwnaia, Abu Graib, Wasit, Anbar and Basrah. These samples were examined by XRD to determine the mineral constituents. Clay fractions were separated for clay mineralogy. The results showed that the clay minerals represent about 40% of the mineral constituents of the samples, dominated by montmorillonite, illite, palygorskite and chlorite having various proportions. The non-clay minerals are represented by calcite and dolomite which present as detrital grains and representing about 32% of the mineral constituents. Quartz comes with about 22% and feldspars with about 5%. The water-soluble salts in the soil samples varied according to the sampling location and represented about 0.3% on average, increasing from north to south. The study showed the relation of the soil mineralogy with source rocks, and the most of the Iraqi soils are the results of erosion, weathering and transported by rivers. The authigenic minerals are locally precipitated from near-surface saline ground waters.