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Examples Of Sedimentary Rock

Examples of Clastic Sedimentary Rocks

Conglomerate

conglomerateis made up of rounded pebbles cemented together. The pebbles have been rounded by the action of moving water. This could be from a river or stream or from waves on a long ago beach.

Because they have been transported by water the pebbles may be from a wide variety of rock types. The size of these rock fragments is over 2 mm in diameter.

After the pebbles have been deposited they are compacted by the sediments that pile up on top of them. Over very long periods of time the pebbles become cemented together by minerals. Silica, calcite, and iron oxides are the most common cementing minerals.

The rounded rock particles in the conglomerate are easily visible to the naked eye.

Conglomerateis made up of rounded pebbles cemented together. The pebbles have been rounded by the action of moving water. This could be from a river or stream or from waves on a long ago beach.

 

Because

6jasper-mookite-australian-mines3232they have been transported by water the pebbles may be from a wide variety of rock types. The size of these rock fragments is over 2 mm in diameter.

 

After the pebbles have been deposited they are compacted by the sediments that pile up on top of them. Over very long periods of time the pebbles become cemented together by minerals. Silica, calcite, and iron oxides are the most common cementing minerals.

 

The rounded rock particles in the conglomerate are easily visible to the naked eye.


Sandstone

sandstone-argillaceousis as its name says sand grains cemented together into solid stone. The grain size of sandstone is 1/16 to 2 mm in diameter.
Sandstone is made up mostly of quartz. There are two reasons for this. First quartz is one of the most abundant minerals on earth. Second is that quartz is very durable. It resists weathering and chemical change.
Silica, calcite, and iron oxides are the most common cementing minerals for sand stone.

These minerals are deposited in the spaces between the sand grains by water.
Over the course of thousands or even millions of years the minerals fill up all of the spaces.
When iron is present in the cementing minerals the sandstone takes on a reddish color.


Silt stone

siltstoneis made from silt of course. Silt is another name for clay and is very fine grained. The grain size is from 1/16 to 1/256 of a millimeter in diameter. It is very similar to sandstone in appearance but with a finer texture.
Once deposited the silt becomes compacted and cemented together into solid stone.
Silica, calcite, and iron oxides are the most common cementing minerals for siltstone. These minerals are deposited in the spaces between the silt grains by water. Over the course of thousands or even millions of years the minerals fill up all of the spaces resulting in solid rock.



Shale

shale is similar to siltstone but with even finer grain size, less than 1/256 of a millimeter in diameter.
It is a very common sedimentary rock.
It is composed of silt or clay.

This is very fine particles of weathered and deconposed rock.
Once deposited the silt becomes compacted and cemented together into solid stone.
Silica, calcite, and iron oxides are the most common cementing minerals for shale.

These minerals are deposited in the spaces between the silt grains by water.
Over the course of thousands or even millions of years the minerals fill up all of the spaces. Shale is usually found in layers.


Examples of Chemical Sedimentary Rocks

Evaporates

Halite

halite1is also known as rock salt. The chemical name is sodium chloride NaCl It is called an evaporate.

It forms in places where sea water has been isolated from the ocean forming a lake.

As the saltwater evaporates in the lake the salt becomes concentrated in the remaining water.

As the water continues to evaporate the lake can no longer hold the same amount of salt.

The salt precipitates out and is deposited as crystallized sodium chloride or salt.



Gypsum

gypsumis an evaporate made of calcium sulfate that has many forms.

Clear flattened crystals are called selenite.

Satin spar and alabaster are also common forms of gypsum.




Carbonates

Limestone

limestoneis made primarily of calcium carbonate or calcite.

The most common source of this calcite is the shells of marine organisms.







Fossiliferous Limestone

fossilis limestone that contains the remains of ancient plants or animals in the form of fossils.








Siliceous Rocks

Chert

chertis a micro crystalline sedimentary rock that is silica rich. It has many forms and colors.








Organic Sedimentary Rocks

Coal

coalis composed of organic matter in the form of plant fragments. Coal can be:
* Lignite is black and has a crumbly consistency.
* Bituminous coal can be dull to shiny and black.
* Anthacite is usually considered metamorphic


Organic Sedimentary Rocks

Sedimentary Rocks

Sedimentary rocks

sedimentare classified in three main groups: clastic, chemical, and organic.

Each group forms in a very unique way by completely different processes.The word Sedimentary comes from the Latin word sedimentum, which means settling. All of the clastic rocks are formed from broken bits and pieces of other existing rocks that settle out of water or air. The broken bits and pieces are called sediments and are caused by weathering.

Weathering
All rocks are subject to weathering. Weathering is anything that breaks the rocks into smaller pieces or sediments. This can happen by the forces of wind, rain, or moving and freezing water.


Deposition
The sediments that form from these actions are often carried to other places by the wind, running water and gravity. As these forces lose energy the sediments settle out of the air or water. As the settling takes place, the rock fragments are graded by size. The larger, heavier pieces settle out first. The smallest fragments travel farther and settle out last. This process of settling out is called deposition.

 

Erosion
The combination of weathering and movement of the resulting sediments is called erosion.
Lithification
Lithification is the changing of sediments into rock. There are two processes involved in this change. They are compaction and cementation.
Compaction occurs after the sediments have been deposited. The weight of the sediments squeezes the particles together. When more and more sediments are deposited on top, the weight on the sediments below increases. Waterborne sediments become so tightly squeezed together that most of the water is pushed out.
Cementation happens when dissolved minerals fill in the spaces between the sediment particles. These liquid minerals act as glue or cement to bind the sediments together.
Clastic sedimentary rocks are further organized according to the size of the sediment particles.
Chemical sedimentary Rocks
Chemical sedimentary rocks are not formed from sediments in the way that clastic sedimentary rocks are. Instead, they are formed from chemicals (elements) dissolved in water. Lakes, rivers, oceans, and ground water all have elemental chemicals dissolved in them.
There are three types of chemical sedimentary rocks:
•    Evaporites
1.    Halite or rock salt
2.    Gypsum
3.    travertine
•    Carbonates
1.    limestones
2.    dolostones
•    Siliceous rocks
1.    chert
Evaporates
Evaporites form when bodies of water evaporate leaving behind deposits of one or more chemicals. Those white deposits on your sinks and faucets are the beginnings of this type of rock.
Another example of evaporate rocks can be found in your kitchen. Most table salt comes from Utah. The Great Salt Lake is the remnant of a vast inland sea that once covered much of the western United States. It is slowly shrinking in size due to evaporation. As the water evaporates the lake can no longer hold the same amount of salt. The salt precipitates out and is deposited as crystallized halite.
This is the basic process for all evaporates. As water evaporates, the remaining water becomes saturated with elements. The water can no longer hold the elements in solution and they crystallize into solid form.
The Carbonates
The carbonates are formed by chemical and biochemical processes. Limestones and dolostones are included in this group. They are made up primarily of two minerals, calcite CaCO3 and dolomite CaMg(CO3)2
Siliceous rocks
The siliceous rocks are dominated by silica SiO2. Silica-secreting organisms like diatoms and radiolarians are responsible for the formation of this type of rock.
Organic sedimentary rocks
Organic sedimentary rocks are composed of organic matter in the form of plant fragments. We usually think of this group of rocks as coal.
•    Lignite is black and has a crumbly consistency.
•    Bituminous coal can be dull to shiny and black.
Rocks are the record, set in stone, of how the earth formed. The clues are all around you. You just need to learn the language and soon you’ll be reading the pages of earth’s history in the rocks that surround you…anywhere you go!

 

Sedimentary Rock Classification
How Do You tell One Sedimentary Rock from Another
Sedimentary rock is classified into two groups based on how they form. They are clastic and chemical.
Clastic sedimentary rock is formed as bits of weathered rock become cemented together. Because all kinds of rock are subject to weathering many different minerals can make up this group of rocks. Clays and quartz are the most common.
Classification of clastic sedimentary rocks is done according to the size of the sediments that make up the rock.

 

Sedimentary Rock Examples


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