IN SITU TESTING OF ROCK HARDNESS AND ITS RELATIONSHIP TO LITHOLOGIC CHARACTERISTICS AND STRUCTURAL ORIENTATION

Weathering studies via the proxy of rock hardness have many challenges. Spatial and temporal scales need to be considered when attempting to extrapolate the compressive strength of mineral surfaces to the potential for landscape development and rate of sediment production. Many chemical and physical properties influence the degree of weathering and hardness of a rock. Attempting to control as many variables as possible can help support correlations spanning spatial scales. In this study we investigated the relationship between rock hardness and lithologic characteristics and structural orientation within the Conococheague Formation near Shepherdstown, WV. The Conococheague Formation is a thick, upper Cambrian aged, algal and mechanically deposited limestone with interbeds of dolostone and siliceous and dolomitic laminations. The formation contains thrombolytic intervals consisting of thick, massive, thrombolitic strata that alternate with ribbons of limestone. Structurally the formation is complex, containing numerous NNE-SSW trending folds and a few WNW bearing faults. In situ rock hardness was measured on the weathered dip surface, strike surface, and freshly exposed dip surface using a type N Schmidt Hammer. Additionally, measurements of aspect, orientation, exposure, and lithology were recorded. A T test (with significance of 95%) showed there is no significant difference of compressive strength between the fresh and dip surfaces, nor is there a significant difference between the dip and strike surfaces. Results of the study highlight the importance of studying the relationship of a rock’s outcrop exposure surfaces and orientation in space and how that may, or may not, influence its weathering and breakdown over time.