Pebbles

Pebbles are small, rounded stones produced by the weathering and transport of larger rocks. By size, pebbles are generally defined as having diameters between about 4 and 64 millimeters. Stones larger than pebbles are classified as cobbles, and smaller ones as granules or sand. Pebbles can be of nearly any rock type, with quartz and quartzite pebbles among the most common in many streams and beaches.

Formation and appearance: Pebbles form when rock fragments are broken down and then transported by water, ice, or wind. During transport, edges are abraded and surfaces are polished, yielding smooth, rounded shapes. Their mineral composition reflects their source rock and may reveal a history of transport and depositional environment.

Geographic occurrence: Pebbles are ubiquitous in riverbeds, floodplains, beaches, and glacial outwash plains. Beach pebbles are often well-rounded and may exhibit polish; river pebbles are commonly well-sorted and rounded.

Uses and significance: In landscaping and construction, pebbles are used as decorative gravel, drainage layers, or paving. They also appear in aquaria and terrariums. In geology, pebble composition and rounding can help reconstruct past energy and transport directions of sedimentary environments. Pebbles form part of the larger category of gravel, and their specific characteristics reflect the conditions under which they were transported and deposited.