Colloquial term for an unusually hard, heavy cue ball made of ceramic instead of the phenolic resin or other modern, resilient plastics most billiard balls are made of. "Rock" cue balls are frequently found on older coin-operated bar tables that do not have magnetic ball-return mechanisms. As with oversized "grapefruit" cue balls, the ball return works because the cue ball is considerably heavier than, and thereby distinguishable from, the object balls. Because of their brittle material, rocks wear out faster that normal cue balls, are prone to chippings, and due to their density also shorten the lifespan of the object balls and the cloth. Their weight has a strong effect on play, as they are difficult to draw (screw), stop and stun, and generate a large amount of smash-through, compared to standard and magnetic cue balls, but do not reduce cut shot accuracy like grapefruit balls.