Pebble
A pebble is a clast of rock with a particle size of 4 to 64 millimeters based on the Krumbein phi scale of sedimentology. It is generally considered to be larger than gravel and smaller than cobble. 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 unusual ecological niches which can provide habitat for a number of rare and endangered species.
Pebbles come in a variety of different colors and textures, and can often have streaks of quartz and different colored sedimentary rock. 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 pebbles. Pebbles left above the high water mark, may have the growth of organisms such as lichen on them, signifying the lack of contact with sea water.
Pebbles can also be found inland where ancient seas used to be cover the land, when seas retreat the rocks become landlocked. Pebbles can also form in rivers, and travel into estuaries where the smoothing continues in the sea.
In: industrial rocks and minerals · Tagged with: construction material, industrial rocks and materials, pebble
Gravel
Gravel is rock that is of a specific particle size range. In geology, gravel is any loose rock that is larger than two millimeters (2mm) in its largest dimension (about 1/12 of an inch) and no more than 63 millimeters (about 2.5 inches). Sometimes gravel is restricted to rock in the 2-4 millimeter range, with pebble being reserved for rock >4-63 millimeters. The next smaller size class in geology is sand, which is >0.063 mm to 2 mm in size. The next larger size is cobble, which is >63 millimeters to 256 millimeters (about 2.5 to 10 inches). One cubic foot (28.32 dm3) of gravel typically weighs about 100 pounds (45 kg).
Gravel is an important commercial product, used in many 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 tarmac; Russia alone has over 400,000 km of gravel-surfaced roads.
In: industrial rocks and minerals · Tagged with: construction material, gravel, industrial rocks and minerals