Marble (toy) - Wikipedia
https://en.m.wikipedia.org/wiki/Marble_(toy)
A marble is a small spherical object often made from glass, clay, steel, plastic, or agate.They vary in size, and most commonly are about 13 mm (1 ⁄ 2 in) in diameter. These toys can be used for a variety of games called marbles, as well being placed in marble runs or races, or created as a form of art. They are often collected, both for nostalgia and for their aesthetic colors.