The Schmidt hammer (SH) test, which is quick, inexpensive, non-destructive and simple to use, has been widely applied to determine hardness and to assess the unconfined compressive strength of rocks. Lithofacies (composition and texture) and environmental conditions (mainly climate) influence the mechanical properties of rock masses as shown by the investigation presented here. To evaluate these effects, a range of carbonate rocks from Al-Ain arid region in the United Arab Emirates were used for extensive in situ and laboratory SH tests. The results expose a wide range of Schmidt hardness rebound (SHRcor) values for both the in situ and the laboratory tests, but show comparable correlation coefficients between the in situ and laboratory natural surface data. This indicates that field SH measurements can be a simple and reliable tool to obtain data on rock mechanical properties; however, caution should be taken in generalization even in a small locality or a region. Although our data are within the wide range of SH values in the published literature, it is apparent that they represent unique values for the rock type investigated and the environment and thereby provide better constraints for engineers in planning for the safety aspects of constructions.