A method of producing graphene sheets and plates from graphitic material including (a) mixing graphitic material particles in a liquid medium to form a suspension; (b) compressing the suspension; (c) directing the compressed suspension through a local constriction into an area of reduced pressure to decompress the suspension in less than 2×10−6 second to a pressure less than 20% of the compression pressure, thereby exfoliating graphene sheets and plates from the graphitic material.