Rotary blast hole drills were observed in several formations at different open pit mines and quarries. Rock samples were collected as near as possible to drilling locations and mechanical and physical properties of the total 22 rock samples were determined. Indentation tests were carried out on the block samples from the same formations, A new drillability index for the prediction of the penetration rates of rotary blast hole drills and the mechanical and physical properties of the rock formations was defined from force-indentation curves of indentation tests. A penetration rate model for rotary for blast hole drills was developed using this drillability index. It was seen that the model was valid for the formations having uniaxial compressive strength over 40 MPa and especially for carbonaceous rocks.