Pebble

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Pebble

A pebble is a clast

Clastic rocks

Clastic rocks are composed of fragments, or clasts, of pre-existing Rock . The term is most commonly, but not uniquely, applied to sedimentary rocks....
of rock

Rock (geology)

In geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock....
with a particle size of 4 to 64 millimeters based on the Krumbein phi scale of sedimentology

Sedimentology

Sedimentology encompasses the study of modern sediments such as sand, mud , and clay, and understanding the processes that deposit them. Sedimentologists apply their understanding of modern processes to interpret geologic history through observations of sedimentary rocks and sedimentary structures....
. It is generally considered to be larger than gravel

Gravel

Gravel is rock that is of a specific particle size range. Specifically, it is is any loose rock that is larger than two millimeters in its largest dimension and no more than 64 millimeters ....
and smaller than cobble

Cobble

Cobble may refer to:* A particular size of rock, larger than gravel* Cobblestone, partially-rounded rocks used for road paving* Hammerstone, a prehistoric stone tool...
. A rock made predominantly of pebbles is termed a conglomerate

Conglomerate (geology)

A conglomerate is a Rock consisting of individual stones that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts....
. 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

Shingle beach

A shingle beach is a beach which is armor with pebbles or small to medium sized cobbles. Typically the stone composition may grade from characteristic sizes ranging from two to 200 millimeters in diameter....
.

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Encyclopedia

A pebble is a clast

Clastic rocks

Clastic rocks are composed of fragments, or clasts, of pre-existing Rock . The term is most commonly, but not uniquely, applied to sedimentary rocks....
of rock

Rock (geology)

Sedimentology

Gravel

Cobble

Conglomerate (geology)

Shingle beach

Armor (hydrology)

Armor, in hydrology and geography is the association of surface pebbles, rocks or boulders with stream beds or beaches. Most commonly hydrology armor occurs naturally; however, a man-made form is usually called riprap, when shorelines or stream banks are fortified for erosion protection with large boulders or sizable manufactured concrete ob...
with respect to wave erosion

Erosion

For morphological image processing operations, see Erosion 'For use of in dermatopathology, see Erosion Erosion is the removal of solids in the natural environment....
, as well as unusual ecological niches which can provide habitat

Habitat

The term habitat has a number of meanings:* Habitat , a place where a species lives and grows** Human habitat, a place where humans live, work or play...
for a number of rare

Rare species

A rare species is an organism which is very uncommon or scarce. This designation may be applied to either a plant or animal taxon, and may be distinct from the term "endangered species" or "threatened species"....
and endangered species

Endangered species

An endangered species is a population of an organism which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters....
.

Pebbles come in a variety of different colors and textures, and can often have streaks of quartz

Quartz

Quartz is the most abundant mineral in the Earth's continental crust . It is made up of a Crystal structure of silica tetrahedra. Quartz has a hardness of 7 on the Mohs scale and a density of 2.65 g/cm?....
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

Tide

Tides are the rising of Earth's ocean surface caused by the tidal forces of the Moon and the Sun acting on the oceans. Tides cause changes in the depth of the marine and estuary water bodies and produce oscillating currents known as tidal streams, making prediction of tides important for coastal navigation ....
, may have the growth of organisms such as lichen

Lichen

Lichens are composite organisms consisting of a symbiosis association of a fungus with a Photosynthesis partner , usually either a green algae or Cyanobacteria ....
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

River

A river is a natural stream of water, usually freshwater, flowing toward an ocean, a lake, or another stream. In some cases a river flows into the ground or dries up completely before reaching another body of water....
, and travel into estuaries

Estuary

An estuary is a semi-enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
where the smoothing continues in the sea.

Pebble

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See also