The method of increasing the hardness of wurtzite crystalline materials is directed to the production of tool bits and inserts having a hardness approaching that of diamond, while simultaneously providing greater toughness and fracture resistance than diamond. The method includes forming a workpiece of boron nitride having a wurtzite crystal structure (wBN), and optionally combining boron nitride having a cubical crystal structure (cBN) with the wBN material. The workpiece is heat-treated by a defocused laser beam moved across the surface at a rate sufficient to preclude melting or deformation of the workpiece. The heated area is quickly quenched by a water jet, and a gas jet immediately follows the laser path to assure separation of the water from the laser contact area. The result is an increase in hardness of about 88%, from an initial hardness of about 40 GPa to a treated hardness of about 75 GPa.