Abstract: Soft hexagonal boron nitride crystals of 200-600 microns platelet size are produced from crystals of less than fifty microns particle size by mixing the small crystals with Li.sub.3 N, simultaneously heating and pressurizing said mixture to a temperature and pressure in a restricted region of the graphitic (hexagonal) boron nitride (GBN) stable region of the pressure-temperature (P-T) phase diagram of boron nitride, cooling and depressurizing said mixture, and separating off the water soluble material present in the mixture to leave a residue of large crystals of boron nitride.