The fracture energy of Sioux quartzite in air and water measured with the wedge-loaded double cantilever beam fracture specimen is found to depend on the angle of the wedge used. The measured fracture energy is greater when the wedge is sharper. This is ascribed to the decrease in the compressive stress acting on the specimen. It is proposed that the compressive stress aids in the formation of the microcracks necessary for crack extension. Measurements of the width of the microcrack zone (visible with the scanning electron microscope) adjacent to the primary crack support this interpretation.