A marble is a small spherical object often made from glass, clay, steel, plastic, or agate. These balls vary in size. Most commonly, they are about 13 mm (1⁄2 in) in diameter, but they may range from less than 1 mm (1⁄30 in) to over 8 cm (3 in), while some art glass marbles for display purposes are over 30 cm (12 in) wide. Marbles can be