The present work deals with the study of the nature and composition of the different geomorphic units of the shore zone of Tobruk coastal area, Libya. The area lies at 150 km from the Egyptian border on the Mediterranean Sea coast and stretches for 40 km from Wadi Elsahal west of Tobruk to Wadi Ras buad in the east. Two field trips (December 2018 and January 2019) were carried out to select areas of interest for geomorphology. Consideration was given to collect and describe different geomorphic units on the coastal zone. These include: sea cliffs, sand beaches, sand dunes, and beachrocks. From these sub-environments, 17 thin sections were prepared for the determination of microfacies and thirty-seven samples were chosen from the exposed different cliffs, beach rock, beach sand, and dunes in the coastal area of Tobruk. The Olympus polarizing microscope BX51 was used for thin sections petrographic description and photomicrographs were taken digitally. The depositional environments and the subsequent diagenetic changes were determined. Microfacies associations of limestones were classified using the classification of Dunham (1962) and the modifications of Embry and Klovan (1971). X–ray powder diffraction analysis was carried out on raw samples for their bulk mineralogy. Samples were finely ground to pass a 200–mesh sieve. X–ray diffractometer type PW3710 at the Metallurgy Institute of Minerals, Helwan, Cairo, Egypt, was used. Instrumental settings employed were Ni–filtered and CuKα radiation at 40 kV and 30 mA. The scanning range was between 2Ɵ 3˚–60˚at scan speed 2Ɵ 2˚/min. The X–ray diffractometer is computerized to measure the peak diffraction in 2Ɵ and d spacing (Å). The identification was confirmed by computer-aided search of the PDF database obtained from the joint committee on Powder Diffraction Standard—International Centre for Diffraction Data (JCPDA–ICDD, 2001). Examination of the 17 thin sections proved the presence of different microfacies associations and the rock cliffs are represented by the Al Khowaymat Formation. These include: echinoderm wackestone, algae echinoderm packstone, sandy peloidal packstone, echinoderm bivalve grainstone, mixed grainstone, echinoderm bivalve floatstone, oncoid rudstone, and echinoderm algae rudstone. These microfacies were deposited in restricted environments such as shallow open lagoons and bays, mid ramp setting, shallow energetic marine conditions with high agitation, inner ramp setting, open and restricted shallow platforms, and finally tidal flats. Mineralogical aspects show that calcite is the predominant carbonate mineral recorded in the rock cliff terraces, while high Mg–calcite is dominant in the beachrocks associated with aragonite and dolomite indicating their recent origin from beach sands. The bulk mineralogy of sand dunes is very significant, reflecting the dominance of carbonate minerals; high Mg–calcite, calcite, aragonite and dolomite over the detrital minerals indicate that they were derived from beach sands.