This paper summarizes the genesis of sedimentary rocks as a basis for the description and better understanding of the results of laboratory tests of breccia samples. Samples of two lithogenetic types of breccia were taken at two locations on the island of Krk, in order to determine their physical and mechanical properties. The samples belong to a subgroup of sedimentary clastic rocks, and their genesis and description described in the paper serve as a basis for a better understanding of the conducted experiments, as well as their results. At the first location, Stara Baska, Krk Island, an in-situ assessment of the strength of the rock mass uniaxial compressive strength was performed using a sclerometer and a geological hammer. Rock mass samples, which will be tested in the laboratory, as well as seawater, which will be used in the dynamic determination of the durability of the rock (eng. Slake Durability Test, SDT), were also collected at the location. Sufficient number of samples for laboratory testing of rock mass weathering using SDT were collected from each location. Point Load Test was performed on all samples prior to the durability test. All experiments were carried out in the Geotechnical Laboratory of the Faculty of Civil Engineering in Rijeka, in accordance with the prescribed norms, including the correctness of the device.