A single crystal diamond grown by microwave plasma chemical vapor deposition has a hardness of 50 90 GPa and a fracture toughness of 11 20 MPa m.sup.1/2. A method for growing a single crystal diamond includes placing a seed diamond in a holder; and growing single crystal diamond at a temperature of about 1000.degree. C. to about 1100.degree. C. such that the single crystal diamond has a fracture toughness of 11 20 MPa m.sup.1/2.