Origin of the glauconite from the Middle Eocene, Qarara Formation, Egypt

• Glauconite pellets are composed of mixed–layer clays, quartz and feldspars.
• The glauconite grains are present in two shapes (spherical and elliptical).
• They are authigenic in origin as evidenced by high sorting.
• They are also less mature as evidenced by the higher expandable layer contents.

Although the Middle Eocene sediments at the Nile Valley, Egypt have been extensively studied, the origin of glauconites in these sediments is still questionable. In this paper, the glauconites that occur in the Qarara Formation were subjected to petrographical and mineralogical studies to assess their origin.Glauconite pellets or grains have been separated from the glauconitic sandy units of the studied three sections. They are present in different colors and different forms. X-ray diffraction analysis indicated that bulk samples are composed of mixed – layer clays (illite-montmorillonite), quartz, microcline, and albite. The separated glauconite grains are present in two shapes, the first is spherical and the second is elliptical, both are green in color with different grades. They are authigenic in origin as evidenced by high sorting, presence of deep or surficial fractures, and as supported to form by alteration of fecal pellets. They are also less mature as evidenced by their pale green color and by the higher expandable layer contents in their mixed-layer clay composition.