In this post, you will learn four characteristics of sedimentary rocks.
So now, let’s get started.
Characteristics of Sedimentary Rocks (Listed and Explained)
Formation Through Lithification
Sedimentary rocks often take a step known as lithification during their formation.
What is lithification, you ask?
Rock debris that has been moved and deposited by physical movement is referred to as lithification.
Abrasion or sorting can cause the rock particles to become rounded or highly sorted during transportation.
A clast is a piece of a rock or mineral turned into small pieces by weathering and erosion the parent rock.
As soon as a clast becomes a part of a larger rock, it is free to move away from it.
Water generally transports them, with sediment deposited on top of them.
The burial stage of lithification involves the deposition of more sediment layers on top of those deposited earlier.
Overlying material exerts pressure on sediments buried by it, resulting in compaction.
In other words, the sediments are “squeezed” from all sides into a smaller volume by the pressure, known as lithostatic pressure.
The lithostatic pressure increases the compactness of the sediment grains.
This reduces the porosity or the space between the sediment grains.
The lithification of living organisms often results in several types of sedimentary rocks.
Coral reefs, shells, and skeletons of marine organisms may be directly lithified into limestone deposits.
The skeletons of marine microorganisms like foraminifera form the foundation of chalk, a type of limestone.
The lithification of plants produces coal and lignite.
Minerals of Sedimentary Rocks
Weathering and erosion are natural processes that occur at the earth’s surface for any rock containing any mineral.
However, minerals found in sedimentary rocks are generally more stable in the earth’s surface environment than others.
Weathering to deposition is the process of winnowing and modifying clasts, which are grains of clastic sediment.
The emergence of more resistant minerals is accompanied by the gradual elimination of weaker and more reactive minerals.
The quartz tends to accumulate during the process, as it is found in the source rocks and has a high degree of hardness, making it relatively resistant to physical breakdown.
It is also resistant to chemical corrosion because quartz does not readily dissolve or chemically alter.
Because of this, beach sand is often the most abundant in quartz minerals.
As minerals precipitate from water in chemical sedimentary rocks, they are generally not transported far before lithification or remain in place.
The erosion and transportation of such mineral sediments are minimal.
As a result, minerals in chemical sedimentary rocks are not winnowed during weathering-to-deposition as they are in clastic sedimentary rocks.
Sometimes, minerals undergo chemical reactions that alter their properties during chemical sedimentation.
Among chemical sedimentary rocks, dolostone is formed in coastal environments when calcite precipitates are altered into dolomite.
Some chemical sedimentary rocks also contain mineraloid solids.
For example, coal is made up of a mineraloid called carbonaceous material.
Mineraloids, including opal, are chemical sedimentary rocks without fully developed crystal lattices.
Sediments of Sedimentary Rocks
As a sedimentary rock, sandstone is among the most common types.
However, there are numerous others.
These are examples of sediments:
- Other rock fragments, usually in sand, silt, or clay, have been worn down to small pieces.
- Organismal remains, or organic materials.
- As water evaporates from a solution, it leaves behind chemical residues.
Weathering occurs mechanically and chemically on rocks at the surface.
As a result, stones are broken up into smaller pieces.
This is called physical weathering.
By contrast, chemical weathering dissolves more brittle minerals.
As a result, mineral elements dissolve in the solution, and new minerals form.
A process known as erosion involves the removal and transportation of sediment by water, wind, ice, or gravity.
Streams carry large volumes of sediment.
Larger particles are carried by flowing water with greater energy.
A rushing river may carry boulders if it is situated on a steep slope.
However, the sediments will no longer be carried with the stream slowing down.
Instead, smaller particles are carried.
Beaches and deserts have sediments deposited on ponds, rivers, and swamps.
Also, glaciers deposit large quantities of sediments.
The wind can also transport sediment through sand in smaller particles.
Determining the type of sedimentary rock that forms will be chosen by the sediment deposited.
In addition, the environment in which sedimentary rock is deposited determines its color.
The Texture of Sedimentary Rocks
During the weathering-to-deposition process, sedimentary texture includes grain size, roundness, and sorting.
However, chemical sedimentary rocks are formed by processes that do not involve the weather-to-deposition process, so there is no widely accepted texture scheme applicable to them.
Below we’ll discuss more on the different textures of sedimentary rocks.
- Clastic Textures: In terms of sedimentary textures, the size, shape, and sorting of sediment grains are described.
- Grain Characteristics: The size of a grain of clastic sediment is determined by its diameter or width. Different sizes of grains have their names.
- Rounding: Depending on their shape, sediment grains can be rounded, angular, or a mixture of both. Brèccias are sedimentary rocks whose angular grains are mostly pebble-sized or larger.
- Sorting: Sorting refers to the size of all the grains being the same. A well-sorted batch has the same size grains. There are sorted sandstones, and there are not sorted sandstones. There is little sorting in conglomerates, which generally contain a variety of grain sizes ranging from sand to pebbles.
The clastic sedimentary texture is also characterized by the packing of the grains, porosity, and rock hardness. This packing of grains procedure applies only to poorly sorted sediments where the finer clasts form a matrix around the coarser ones. In the case of clast-supported packing, each large grain touches another.
In matrix-supported packing, the coarse grains are separated and not in contact with one another, and the more refined grains are in between.
Porosity measures how much space between sediment grains exists in a rock or sediment.
Hardness refers to the ability of a stone to be broken apart.
For instance, claystone is harder than shale.
These sedimentary rocks are called secondary rocks due to their formation by sediments from other rocks that have been denuded and deposited by the forces of gradation.
They tend to be noncrystalline.
Due to the deposition of sediments, they are soft and have multiple layers.