The speed of the drilling, metres per hour
The limit for the strength of the rocks during the compression, kilograms per square centimetre

DRILLABILITY of the rocks (EN: rock drillability; DE: Bohrbarkeit der Gesteine, Bohrvermogen von Gesteinen; FR: forabilite de roches; ES: perforabilidad de las rocas; RU: буримость) is the resistance of the rocks against the destruction during the process of the drilling. The drillability is evaluated according to the speed of the drilling (the penetration per the unit of time; see the Figure), and according to the time and to the energy consumption for the drilling through the unit of the length within the bore of the borehole or of the blasthole, under the standard conditions during the conducting of the experiment for the each type of the drilling machine. The drillability worsens itself with the increasing of the density, strength, toughness, hardness, and abrasiveness of the rocks, and also depends on the mineral composition, structure of the rocks, and thermodynamic conditions, under which they are located. For the different types of the rock-destructing tools, and of the methods for the drilling, there have been developed the scales of measurement for the drillability. For the transition from one scale to another, and also from the standard conditions for the drilling to the non-standard conditions, there exist the correctional coefficients, and the generalized classifications for the rocks according to the drillability. Within all the classifications, they divide the rocks according to the drillability into the easy-drillable rocks (for example, the mineral coal), the intermediate-drillable rocks (marls), the difficult-drillable rocks (peridotite) and the very difficult-drillable rocks (the ferruginous quartzites). The drillability is taken into account during the valuation of the labour for the workers, during the evaluation for the performance of the drilling, during the choice for the rock-destructing tools, for the quantity of the drilling installations, during the planning and organization for the drilling works under the specific mining-geological conditions.