Natural-color black diamonds generally are completely opaque with a high luster, which provides them with a metallic appearance. The color is due to an intense aggregation of clouds of extremely small mineral inclusions, which include graphite, pyrite and hematite. They also typically feature cleavages or fractures, which are stained black or have become black because of graphitization. They are difficult to cut and polish, and need to be handled with considerable care. A variety of black diamonds is Carbonado, which is a blend of diamond, graphite, and amorphous carbon.