Pebble vs. Gravel

Main Difference

The main difference between Pebble and Gravel is that the Pebble is a clast of rock (between 4-64 mm in diameter according to Wentworth-Udden scale) (for individual members of this granular material, see Q56816802) and Gravel is a mix of crumbled stone (grain size range = 2-63 mm according to ISO 14688)

• Pebble

  A pebble is a clast of rock with a particle size of 4 to 64 millimetres based on the Krumbein phi scale of sedimentology. Pebbles are generally considered larger than granules (2 to 4 millimetres diameter) and smaller than cobbles (64 to 256 millimetres diameter). A rock made predominantly of pebbles is termed a conglomerate. Pebble tools are among the earliest known man-made artifacts, dating from the Palaeolithic period of human history.

  A beach composed chiefly of surface pebbles is commonly termed a shingle beach. This type of beach has armoring characteristics with respect to wave erosion, as well as ecological niches that provide habitat for animals and plants.

  Inshore banks of shingle (large quantities of pebbles) exist in some locations, such as the entrance to the River Ore, where the moving banks of shingle give notable navigational challenges.Pebbles come in various colors and textures and can have streaks, known as veins, of quartz or other minerals. Pebbles are mostly smooth but, dependent on how frequently they come in contact with the sea, they can have marks of contact with other rocks or other pebbles. Pebbles left above the high water mark may have growths of organisms such as lichen on them, signifying the lack of contact with seawater.

• Gravel

  Gravel is a loose aggregation of rock fragments. Gravel is classified by particle size range and includes size classes from granule- to boulder-sized fragments. In the Udden-Wentworth scale gravel is categorized into granular gravel (2 to 4 mm or 0.079 to 0.157 in) and pebble gravel (4 to 64 mm or 0.2 to 2.5 in). ISO 14688 grades gravels as fine, medium, and coarse with ranges 2 mm to 6.3 mm to 20 mm to 63 mm. One cubic metre of gravel typically weighs about 1,800 kg (or a cubic yard weighs about 3,000 pounds).

  Gravel is an important commercial product, with a number of applications. Many roadways are surfaced with gravel, especially in rural areas where there is little traffic. Globally, far more roads are surfaced with gravel than with concrete or asphalt; Russia alone has over 400,000 km (250,000 mi) of gravel roads. Both sand and small gravel are also important for the manufacture of concrete.