Which of the following materials is not suitable to be used to sharpen a dental instrument?

Silicon carbide (SiC) is widely used as an industrial abrasive. It is the most commonly used material for grinding wheels and "sandpapers," as well as for sharpening stones. It is hard enough to cut steel effectively, but not hard enough to sharpen carbide instruments. SiC stones are available in many shapes in coarse and medium grits, but not in fine grits. As a result, they are not as suitable as other materials for final sharpening of dental instruments. Ref: Sturdevant's art and science of operative dentistry. 4th edition page 317