Eight soil profiles were chosen to represent some soils of four locations (El-Kharga oasis, EL-Dakhla oasis, El-Zaiyat plain and Gharb El-Mawhub) in the New Valley governorate, Egypt. Studies of the mineralogical composition of the sand fraction were performed to evaluate the origin, uniformity and weathering status of these soils. X-ray diffraction technique as well as transmission and scanning electron microscopy were also used to identify the clay mineral suits of these soils.
The obtained data reveal that the texture class of the studied surface samples differs from sandy loam, silt loam and clay with a finer texture in Gharb El-Mawhub and El-Dakhla and a coarser one in El-Kharga and El-Zaiyat. Most of these samples are moderately to strongly saline with low calcium carbonate and organic matter in most locations. Gypsum content is low and tends to be free in El-Kharga and El-Zaiyat. The cation exchange capacity (CEC) values of these soils were found to be in accord with their fine particle content (clay and silt). Soil reaction (pH) tends to be mildly to moderately alkaline in most locations. The studied soils are classified according to Soil Taxonomy as: Typic Torriorthents, Typic Torrifluvents, Gypsic Haplosalids and Typic Haplosalids.
Microscopic examination of the sand fraction reveals that the minerals of the light fraction are mainly dominated by quartz followed by calcite beside small amounts of feldspars. On the other hand, opaque minerals dominate the heavy fraction of all studied soils in most locations. The non-opaques are composed essentially of zircon, epidotes, pyroxenes, tourmaline and amphiboles and are present in relatively high amounts. Staurolite, rutile and garnet are found in pronounced amounts while kyanite and biotite are found in minor quantities.
Uniformity and weathering ratios indicate that the soils are heterogeneous, either due to their multi-origin and/or to their formation from parent materials of heterogeneous nature. Thus, the soils are weakly developed, pedogenically young and are formed from different sources.
Smectites (montmorillonite), kaolinites, illite and playgorskite are present in most cases. The predominant clay minerals of the shale deposit in El-Kharga oasis and El-Zaiyat plain are smectites (montmorillonite) with traces of illite and kaolinite. Clay separated from EL-Dakhla oasis is illite, playgorskite and kaolinite, while Gharb El-Mawhub soils have kaolinite as the dominant clay mineral, with small amount of sepiolite and chlorite in some samples. Interstratified minerals are detected in low amounts or as traces in some samples. Quartz and feldspars occur in the clay fraction of most samples in very small amounts.