A clay court is a tennis court that has a playing surface made of crushed stone, brick, shale, or other unbound mineral aggregate. The French Open uses clay courts, the only Grand Slam tournament to do so. Clay courts are more common in Continental Europe and Latin America than in North America, Asia-Pacific or Britain. Two main types exist: red clay, the more common variety, and green clay, also known as "rubico", which is a harder surface. Although less expensive to construct than other types of tennis courts, the maintenance costs of clay are high as the surface must be rolled to preserve flatness.