pebble

geology

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July 1, 2026

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A pebble is a small, typically rounded stone, often smoothed by water action. In geology, pebbles are classified as fragments between 4 and 64 millimeters in diameter, falling within the broader category of gravel. Gravel itself is an aggregate of rock fragments coarser than sand.123

Pebbles can also refer to transparent, colorless quartz, known as rock crystal. The term "pebbly" describes a surface that is rough, uneven, or irregular, rather than smooth. The verb "to pebble" can mean to pelt with pebbles, to pave with them, or to create a grainy texture on a material like leather.145

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gravel
…gravel range in size from pebbles (4–64 mm [0.16–2.52 inches] in diameter), through cobbles (64–256 mm [2.52–10.08 inches]), to boulders (larger than 256 mm). The rounding of gravel results from abrasion in the course of transport by streams or from milling by the sea. Gravel deposits accumulate in parts of…
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…gravel range in size from pebbles (4–64 mm [0.16–2.52 inches] in diameter), through cobbles (64–256 mm [2.52–10.08 inches]), to boulders (larger than 256 mm). The rounding of gravel results from abrasion in the course of transport by streams or from milling by the sea. Gravel deposits accumulate in parts of…
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sand dune
Sands
…than sands, such as small pebbles, only form dunelike features when there are strong and persistent winds, as in coastal Peru, and these coarse-grained features are generally known as granule ripples rather than dunes. Larger particles, such as small boulders, can be moved by the wind only on slippery surfaces…
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…than sands, such as small pebbles, only form dunelike features when there are strong and persistent winds, as in coastal Peru, and these coarse-grained features are generally known as granule ripples rather than dunes. Larger particles, such as small boulders, can be moved by the wind only on slippery surfaces…
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desert pavement
…other salts that cement the pebbles together to form a desert conglomerate. The pebbles often are so packed and smooth that no more wind deflation can occur; in the Sahara such areas are generally followed by caravan routes. A similar area is the hammada, in which wind has removed most…
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…other salts that cement the pebbles together to form a desert conglomerate. The pebbles often are so packed and smooth that no more wind deflation can occur; in the Sahara such areas are generally followed by caravan routes. A similar area is the hammada, in which wind has removed most…
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