Pebble

Pebble is a clast of rock with a particle size of 4 to 64 millimeters based on the Krumbein phi scale of sedimentology. This size sits between gravel and cobble. A pebble is generally considered to be larger than a granule (2 to 4 millimeters in diameter) and smaller than a cobble (64 to 256 millimeters in diameter).

Pebbles are often smooth and rounded due to abrasion by water or wind action. They are commonly found on beaches, in riverbeds, and in glacial deposits. The composition of pebbles varies greatly depending on the source rock and geological history of the area. Common pebble compositions include sedimentary rocks like sandstone, limestone, and shale; igneous rocks like granite and basalt; and metamorphic rocks like gneiss and schist.

The shape and roundness of pebbles can provide information about the distance and duration of transport from their original source. For example, well-rounded pebbles suggest extensive transport and abrasion, while angular pebbles indicate shorter transport distances.

Pebbles have a variety of uses, including decorative purposes in landscaping and construction, as aggregate in concrete, and in some art forms. Historically, pebbles have also been used as tools and in games.