Rock samples from the Baglum-Kosrelik area, 30 km north of Ankara, Turkey have been studied petrographically in detail to differentiate between nodular limestones and hardgrounds. However, it is found that petrographic criteria alone may not always be used to differentiate between nodular limestones and true hardgrounds. Distinction between hardgrounds and other well indurated carbonate rocks can be made based upon the strength properties of the rocks, including uniaxial compressive strengths, triaxial compressive strengths, modulus ratios, and elastic constant ratios. This study showed that rock petrophysical characteristics could be used, to develop criteria for distinguishing hardgrounds. For example, strength tests using the International Society for Rock Mechanics result in very high strength and extreme. hardness values, with a minimum uniaxial compressive strength value of 130 MPa with 10, % standard deviation, therefore the rock can be classified as "true" hardground. Classification of these carbonates in this I manner would facilitate quantitative discussions between hardground carbonate petrographers and engineering geologists. Hardgrounds throughout the world then could be tested and classified accordingly.