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Sedimentary Rocks Facts & Worksheets

A sedimentary rock is a classification of rock that forms from layers of sediments deposited and consolidated at the bottom of oceans, lakes, or other bodies of water.

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Sedimentary rocks arise from pre-existing rock deposits or fragments of once-living organisms that collect on the Earth’s surface. If sediment is submerged deep, it becomes compressed and cemented, resulting in sedimentary rock. Clastic, Biologic, and Chemical are the three types of sedimentary compacted rocks.

See the fact file below for more information on sedimentary rock, or you can download our 24-page Sedimentary Rocks worksheet pack to utilise within the classroom or home environment.

Key Facts & Information

OVERVIEW

  • Sedimentary rocks are created by accumulating or depositing organic or mineral particles at the Earth’s surface, followed by cementation. Sedimentation refers to the mechanisms that lead these particles to settle in situ. 
  • Sediment is the particles that make up a sedimentary rock and can be made up of biological detritus (organic) or geological detritus (minerals). 
  • Weathering and erosion of existing rocks, or the solidification of molten lava blobs spewed by volcanoes, produced the geological debris.
  • Water, wind, ice, or mass movement convey geological debris to the site of deposition, which is referred to as an agent of denudation. 
  • Biological detritus was created by the bodies and parts (primarily shells) of extinct aquatic species hanging in the water and slowly stacking up on the surface of water bodies (marine snow). Sedimentation can also occur when dissolved minerals precipitate from a solution of water.
  • The sedimentary rock covering the Earth’s crust’s continents is broad (73% of the Earth’s current land area) yet accounting for just 8% of the crust’s volume. Sedimentary rocks are shallow veneers on top of an igneous and metamorphic crust.
  • Sedimentary rocks are formed as strata in layers, creating a bedding structure. Sedimentary rocks are commonly found in massive formations known as sedimentary basins. Sedimentary rocks have also been detected on Mars.

THE PROCESS OF CREATION OF SEDIMENTARY ROCKS

  • Erosion, weathering, dissolving, precipitation, and lithification are the principal geological processes resulting in sedimentary rock formation.
  • Wind and rain, which gradually break down massive boulders into smaller ones, are examples of erosion and weathering. Erosion and weathering degrade boulders and even mountains into sediments like sand and mud.
  • Dissolution is a type of weathering, namely chemical weathering. Water that is slightly acidic progressively wears away stone in this method. These three processes produce the building blocks for new sedimentary rocks.
  • Precipitation and lithification are procedures that result in the formation of new rocks or minerals.
  • The production of minerals and rocks from chemicals that precipitate from water is known as precipitation. For example, as a lake dries up over thousands of years, mineral deposits form; this is what happened in California’s Death Valley.
  • Furthermore, lithification is how clay, sand, and other sediments on the ocean’s or other bodies of water’s bottom are gradually compressed into rocks by the weight of overlying sediments.

PROPERTIES

COLOR

  • Iron, a metal having two primary oxides: iron (II) oxide and iron (III) oxide, is frequently responsible for the hue of sedimentary rocks. Only under low oxygen (anoxic) conditions can iron (II) oxide (FeO) develop, giving the rock a grey or greenish appearance.
  • In a higher oxygen environment, iron (III) oxide (Fe2O3) is commonly seen in the form of the mineral hematite, which provides the rock a reddish to brownish tint.
  • Rocks in dry continental areas are in direct touch with the atmosphere, and oxidation is a significant process, turning the rock red or orange.
  • Red beds are thick layers of red sedimentary rocks developed in dry settings. However, a red hue does not always indicate that the rock evolved in a continental or dry environment.
  • The presence of organic substances can cause a rock to be black or grey in hue. Organic material comprises deceased creatures, most of which are plants. Usually, such material degrades by oxidation or bacterial action. However, organic material cannot decompose in anoxic conditions, leaving black sediment rich in organic material.
  • For example, it can happen at the bottom of deep oceans and lakes. Because there is minimal water mixing in such situations, oxygen from surface water is not transported down, and the deposited sediment is often fine black clay. As a result, dark rocks rich in organic content are frequently shale.

TEXTURE

  • Texture refers to the size, shape, and positioning of clasts (the original bits of rock) in silt. The surface of a rock is a small-scale attribute that influences many of its large-scale qualities, including density, porosity, and permeability.
  • The fabric of the rock refers to the 3D orientation of the clasts. The size and shape of clasts indicate the speed and direction of current in the sedimentary environment that carried the clasts from their origin; fine, calcareous mud settles only in calm water, whereas gravel and bigger clasts are only moved by fast-flowing water.
  • The Wentworth scale is commonly used to indicate the grain size of a rock, while other scales are also employed. Because rock is made up of clasts of varying sizes, the grain size can be stated as a volume or diameter and is always an average number.
  • The statistical distribution of grain sizes varies by rock type and is defined by a feature known as rock sorting. When all clasts are around the same size, the rock is said to be ‘well-sorted,’ and when there is considerable variance in grain size, the rock is said to be ‘poorly sorted.’
  • The shape of the clasts might reveal information about the rock’s origin. Coquina, a rock formed of clasts of shattered shells, can develop only in active water. May use four parameters to characterize the shape of a class:
  • Surface texture refers to the degree of small-scale relief on a grain’s surface that is too tiny to alter the overall form. Eolian sandstones, for example, have frosted grains coated with small-scale cracks.
  • Rounding defines the overall smoothness of a grain’s form.
  • Sphericity defines how close the grain is to a sphere.
  • Grain form defines the grain’s three-dimensional shape.
  • Chemical sedimentary rocks have a non-clastic structure and are entirely composed of crystals. Only the average diameter of the crystals and fabric diameter are required to characterize such a texture.

FOSSILS

  • Fossils are typically discovered in sedimentary rock, one of the three primary rock forms. Unlike many other igneous and metamorphic rocks, Sedimentary rocks occur at temperatures and pressures that do not obliterate fossil traces, and these fossils are frequently only visible under magnification.
  • In nature, dead creatures are usually promptly eliminated by scavengers, bacteria, decaying, and erosion, but in rare cases, these natural processes cannot occur, resulting in fossilization.
  • When the sedimentation rate is strong (such that a carcass is swiftly buried), in anoxic conditions (where a few bacterial activities occur), or when the creature has a rigid skeleton, fossilization increases. More significant, well-preserved fossils are uncommon.

THREE BASIC TYPES OF SEDIMENTARY ROCKS

CLASTIC SEDIMENTARY ROCKS

  • Clastic sedimentary rocks are weathered bits (clasts) of pre-existing rocks. The particles range from tiny clay to massive boulders, and the size of the clasts decides their names. The minuscule granules are called clay, next silt, and sand. Pebbles are grains that are greater than 2 millimeters in length.
  • Breccia, made of massive (above two-millimeter diameter) angular particles, is an example of clastic sedimentary rock. It can fill the gaps between the vast shards with a grid of tiny particles or mineral cement, which will bond the rock together.
  • Sandstone is another clastic sedimentary rock composed primarily of sand-sized (1/16 to 2-millimeter diameter) weathering particles. Beaches, deserts, flood plains, and deltas are examples of environments where vast volumes of sand can collect.
  • Arches National Park in Utah and Grand Canyon National Park in Arizona include some of the best examples of clastic sedimentary rock.

BIOLOGIC SEDIMENTARY ROCKS

  • When live creatures die, they pile up and are crushed and cemented together to produce biologic sedimentary rocks.
  • Coal (accumulated carbon-rich plant material) and limestone and coquina are examples of biologic sedimentary rocks (rocks made of marine organisms).
  • May find excellent examples of biologic sedimentary rock in national parks such as Biscayne Bay National Park in Florida and Guadalupe Mountains National Park in Texas.

CHEMICAL SEDIMENTARY ROCKS

  • Chemical sedimentary rocks arise due to chemical precipitation, which begins when water flowing through rock dissolves certain minerals.
  • May find chemical sedimentary rocks in various environments, including the ocean, deserts, and caverns. Most limestone, for example, develops at the ocean’s bottom from the precipitation of calcium carbonate and the remnants of marine creatures with shells.
  • If limestone is discovered on land, it is thought that the region was formerly underwater. Cave formations are also sedimentary rocks, although they form differently.
  • Stalactites and stalagmites develop when water travels through bedrock and takes up calcium and carbonate ions. When chemical-rich water enters a cave, it evaporates and leaves behind calcium carbonate on the ceiling, making a stalactite, or on the cave floor, generating a stalagmite.
  • When water evaporates, these minerals are transported away from their origin and eventually returned to the soil or precipitated.
  • Visit Oregon Caves National Monument in Oregon, Carlsbad Caverns National Park in New Mexico, and White Sands National Monument in New Mexico to see examples of chemical sedimentary rocks.

IMPORTANCE OF STUDYING SEDIMENTARY ROCKS

  • Studying sedimentary rocks and rock strata gives subsurface information valuable for civil engineering, such as the development of roads, housing, tunnels, canals, and other structures. Sedimentary rocks are also significant natural resource sources, such as coal, fossil fuels, drinking water, and ores.
  • The succession of sedimentary rock layers is the primary source for comprehending Earth’s past, including paleogeography, paleoclimatology, and life history.
  • Sedimentology is the scientific study of the characteristics and origins of sedimentary rocks. Sedimentology is a branch of geology and physical geography that intersects with other Earth science disciplines such as pedology, geomorphology, geochemistry, and structural geology.

Sedimentary Rocks Worksheets

This is a fantastic bundle which includes everything you need to know about sedimentary rocks across 24 in-depth pages. These are ready-to-use Sedimentary Rocks worksheets that are perfect for teaching students about sedimentary rock which is a classification of rock that forms from layers of sediments deposited and consolidated at the bottom of oceans, lakes, or other bodies of water. These rocks are formed from sediments such as minerals and other organic matter.

Complete List Of Included Worksheets

  • Sedimentary Rocks Facts
  • The Right Terms
  • Forming Process
  • The Earth and Its Rocks
  • Rock or Roll
  • Classify The Rocks
  • Odd One Out
  • Sedimentary Blanks
  • In My Own Words
  • How Important?
  • Sedimentary Song

Frequently Asked Questions

What are sedimentary rocks?

Sedimentary rocks arise from pre-existing rock deposits or fragments of once-living organisms that collect on the Earth’s surface. 

What are the geological processes that lead to the creation of sedimentary rocks?

Erosion, weathering, dissolving, precipitation, and lithification are the principal geological processes resulting in sedimentary rock formation.

What are clastic sedimentary rocks?

Clastic sedimentary rocks are weathered bits (clasts) of pre-existing rocks. The particles range from tiny clay to massive boulders, and the size of the clasts decides their names. The minuscule granules are called clay, next silt, and sand. Pebbles are grains that are greater than 2 millimeters in length.

Which type of sedimentary rock is coal?

Coal (accumulated carbon-rich plant material) and limestone and coquina are examples of biologic sedimentary rocks (rocks made of marine organisms).

Why studying sedimentary rocks are essential?

Studying sedimentary rocks and rock strata gives subsurface information valuable for civil engineering, such as the development of roads, housing, tunnels, canals, and other structures. Sedimentary rocks are also significant natural resource sources, such as coal, fossil fuels, drinking water, and ores.

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