A cobble (sometimes a cobblestone) is a clast of rock defined on the Udden–Wentworth scale as having a particle size of 64–256 millimeters (2.5–10.1 in), larger than a pebble and smaller than a boulder. Other scales define a cobble´s size differently. A rock made predominantly of cobbles is termed a conglomerate. Cobblestone is a building material based on cobbles.
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