... ,such as clay,soft mudstone,shale,salt,loose sands,etc.437/4470.35-0.9150-70very Soft ... high drillability,such as mudstone,salt,soft limestone, sands,etc.517/5270.35-1.0140-50Soft formation with ... high drillability,such as mudstone,salt,soft limestone,sands,etc535/5450.35-1.0150-60medium soft with harder ... high abrasiveness such as hard limestone,dolomite,firm sands,etc827/8370.7-1.270-40very hard with ...