* Shales with a density less than approximately 2.1 g/cm<sup>3</sup> deform ductilely and not by brittle failure at the range of confining pressures found in most sedimentary basins. | * Shales with a density less than approximately 2.1 g/cm<sup>3</sup> deform ductilely and not by brittle failure at the range of confining pressures found in most sedimentary basins. |