Clastic rock

A thin section of a clast (sand grain), derived from a basalt scoria. Vesicles (air bubbles) can be seen throughout the clast. Plane light above, cross-polarized light below.  Scale box is 0.25 mm.
Claystone from Montana
Conglomerate
Breccia. Notice the angular nature of the large clasts
Sandstone from Lower Antelope Canyon
Basalt breccia, green groundmass is composed of epidote
Red mudrock
Black Shale

Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock.

- Clastic rock
A thin section of a clast (sand grain), derived from a basalt scoria. Vesicles (air bubbles) can be seen throughout the clast. Plane light above, cross-polarized light below.  Scale box is 0.25 mm.

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Wentworth grain size chart from United States Geological Survey Open-File Report 2006-1195: Note size typos; 33.1mm is 38.1 & .545mm is .594

Grain size

Wentworth grain size chart from United States Geological Survey Open-File Report 2006-1195: Note size typos; 33.1mm is 38.1 & .545mm is .594
Beach cobbles at Nash Point, South Wales

Grain size (or particle size) is the diameter of individual grains of sediment, or the lithified particles in clastic rocks.

Cut slab of sandstone showing Liesegang banding

Sandstone

Cut slab of sandstone showing Liesegang banding
Paradise Quarry, Sydney, Australia
Grus sand and the granitoid from which it is derived
Photomicrograph of a volcanic sand grain; upper picture is plane-polarised light, bottom picture is cross-polarised light, scale box at left-centre is 0.25 millimeter. This type of grain would be a main component of a lithic sandstone.
Schematic QFL diagram showing tectonic provinces
Cross-bedding and scour in sandstone of the Logan Formation (Lower Carboniferous) of Jackson County, Ohio
Red sandstone interior of Lower Antelope Canyon, Arizona, worn smooth by erosion from flash flooding over thousands of years
The Main Quadrangle of the University of Sydney, a so-called sandstone university
Sandstone statue Maria Immaculata by Fidelis Sporer, around 1770, in Freiburg, Germany
17,000 yr old sandstone oil lamp discovered at the caves of Lascaux, France
Alcove in the Navajo Sandstone
Kokh-type tombs cut into the multicoloured sandstone of Petra
Sand grains of quartz with hematite coating providing an orange colour

Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains.

Boulder of conglomerate with cobble-sized clasts. Rock hammer for scale.

Conglomerate (geology)

Boulder of conglomerate with cobble-sized clasts. Rock hammer for scale.
Carmelo Formation (conglomerate) at Point Lobos
A conglomerate at the base of the Cambrian in the Black Hills, South Dakota.
Section of polymict conglomerate from offshore rock core, Alaska, approximate depth 10,000 ft.
Fanglomerate in Death Valley National Park

Conglomerate is a clastic sedimentary rock that is composed of a substantial fraction of rounded to subangular gravel-size clasts.

Close view

Pebble

Close view
Pebbles on a shingle beach
Differently coloured pebbles on Rethymno beach, Crete
Similarly coloured pebbles, Nainital Lake, India
A walkway decorated with pebbles set into concrete
Pebbles given a rounded shape by wave action
Beach pebbles made of halite; western Dead Sea coast, Israel
Pebbles on a beach at Broulee, Australia

A pebble is a clast of rock with a particle size of 4-64 mm based on the Udden-Wentworth scale of sedimentology.

Beach cobbles (Nash Point, Wales)

Cobble (geology)

Beach cobbles (Nash Point, Wales)
Sandy conglomerate with cobbles in the Hazeva Formation (Miocene) of southern Israel
Beach cobbles (France)

A cobble (sometimes a cobblestone) is a clast of rock defined on the Udden–Wentworth scale as having a particle size of 64 - 256 mm, larger than a pebble and smaller than a boulder.

This balancing boulder, "Balanced Rock", stands in Garden of the Gods park in Colorado Springs, Colorado, United States.

Boulder

Rock fragment with size greater than 25.6 cm in diameter.

Rock fragment with size greater than 25.6 cm in diameter.

This balancing boulder, "Balanced Rock", stands in Garden of the Gods park in Colorado Springs, Colorado, United States.
Boulder in British Columbia, Canada
Kämmenkivi stone on the Pisa hill in Kuopio, Finland

Boulder-sized clasts are found in some sedimentary rocks, such as coarse conglomerate and boulder clay.

Cross beds in siliciclastic shoreface sediment (Agadir-Essaouira Basin, Morocco)

Siliciclastic

Cross beds in siliciclastic shoreface sediment (Agadir-Essaouira Basin, Morocco)

Siliciclastic (or siliclastic ) rocks are clastic noncarbonate sedimentary rocks that are composed primarily of silicate minerals, such as quartz or clay minerals.

Dust blowing from the Sahara Desert over the Atlantic Ocean towards the Canary Islands

Sediment transport

Movement of solid particles , typically due to a combination of gravity acting on the sediment, and/or the movement of the fluid in which the sediment is entrained.

Movement of solid particles , typically due to a combination of gravity acting on the sediment, and/or the movement of the fluid in which the sediment is entrained.

Dust blowing from the Sahara Desert over the Atlantic Ocean towards the Canary Islands
Sand blowing off a crest in the Kelso Dunes of the Mojave Desert, California.
Toklat River, East Fork, Polychrome overlook, Denali National Park, Alaska. This river, like other braided streams, rapidly changes the positions of its channels through processes of erosion, sediment transport, and deposition.
Congo river viewed from Kinshasa, Democratic Republic of Congo. Its brownish color is mainly the result of the transported sediments taken upstream.
Sand ripples, Laysan Beach, Hawaii. Coastal sediment transport results in these evenly spaced ripples along the shore. Monk seal for scale.
A glacier joining the Gorner Glacier, Zermatt, Switzerland. These glaciers transport sediment and leave behind lateral moraines.
Suspended sediment from a stream emptying into a fjord (Isfjorden, Svalbard, Norway).
Original Shields diagram, 1936
Streamlines around a sphere falling through a fluid. This illustration is accurate for laminar flow, in which the particle Reynolds number is small. This is typical for small particles falling through a viscous fluid; larger particles would result in the creation of a turbulent wake.
The logarithmic Hjulström curve
A schematic diagram of where the different types of sediment load are carried in the flow. Dissolved load is not sediment: it is composed of disassociated ions moving along with the flow. It may, however, constitute a significant proportion (often several percent, but occasionally greater than half) of the total amount of material being transported by the stream.

Sediment transport occurs in natural systems where the particles are clastic rocks (sand, gravel, boulders, etc.), mud, or clay; the fluid is air, water, or ice; and the force of gravity acts to move the particles along the sloping surface on which they are resting.

Basalt breccia in the Canary Islands; green groundmass is composed of epidote

Breccia

Sedimentary rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix.

Sedimentary rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix.

Basalt breccia in the Canary Islands; green groundmass is composed of epidote
Megabreccia (left) at Titus Canyon Narrows, Death Valley National Park, California
Tertiary breccia at Resting Springs Pass, Mojave Desert, California
Unusual breccia cemented by azurite and malachite, Morenci Mine, Arizona
Alamo bolide impact breccia (Late Devonian, Frasnian) near Hancock Summit, Pahranagat Range, Nevada
Hydrothermal breccia in the Cloghleagh Iron Mine, near Blessington in Ireland, composed mainly of quartz and manganese oxides, the result of seismic activity about 12 million years ago
Silicified and mineralized breccia. Light gray is mostly dolomite with a little translucent quartz. Dark gray is jasperoid and ore minerals. Veinlet along lower edge of specimen contains sphalerite in carbonates. Pend Oreille mine, Pend Oreille County, Washington
Breccia statue of the Ancient Egyptian goddess Tawaret

Clastic rocks are also commonly found in shallow subvolcanic intrusions such as porphyry stocks, granites and kimberlite pipes, where they are transitional with volcanic breccias.

Sediment

Naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles.

Naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles.

Sediment in the Gulf of Mexico
Sediment off the Yucatán Peninsula
Schematic representation of difference in grain shape. Two parameters are shown: sphericity (vertical) and rounding (horizontal).
Comparison chart for evaluating roundness of sediment grains
Sediment builds up on human-made breakwaters because they reduce the speed of water flow, so the stream cannot carry as much sediment load.
Glacial transport of boulders. These boulders will be deposited as the glacier retreats.
Modern asymmetric ripples developed in sand on the floor of the Hunter River, New South Wales, Australia. Flow direction is from right to left.
Sinuous-crested dunes exposed at low tide in the Cornwallis River near Wolfville, Nova Scotia
Ancient channel deposit in the Stellarton Formation (Pennsylvanian), Coalburn Pit, near Thorburn, Nova Scotia.
Glacial sediments from Montana
Holocene eolianite and a carbonate beach on Long Island, Bahamas

Littoral sands (e.g. beach sands, runoff river sands, coastal bars and spits, largely clastic with little faunal content)