ROCKS
What are rocks?
Rocks are made of grains that fit together. Each grain in the rock is made from a mineral, which is a chemical compound. The grains in a rock can be different colours, shapes and sizes.
Some types of rock have interlocking grains that fit tightly together. Granite is a rock with interlocking grains. Other types of rock have rounded grains. Sandstone is a rock with rounded grains.
How many types of Rocks are there?
There are three main types of rock: sedimentary, igneous and metamorphic.
1) Sedimentary Rocks-Formation
A river carries, or transports, pieces of broken rock as it flows along. When the river reaches a lake or the sea, its load of transported rocks settles to the bottom. We say that the rocks are deposited. The deposited rocks build up in layers, called sediments. This process is called sedimentation.
The weight of the sediments on top squashes the sediments at the bottom. This is called compaction. The water is squeezed out from between the pieces of rock and crystals of different salts form.
The crystals form a sort of glue that sticks or cements the pieces of rock together. This process is called cementation.
These processes eventually make a type of rock called sedimentary rock. It may take millions of years for sedimentary rocks to form.
Therefore, these are the different processes in order:
1) sedimentation → 2) compaction → 3) cementation
2) Igneous rocks-Formation
The inside of the Earth is very hot - hot enough to melt rocks. Molten (liquid) rock forms when rocks melt. The molten rock is called magma. When the magma cools and solidifies, a type of rock called igneous rock forms.
Igneous rocks contain randomly arranged interlocking crystals. The size of the crystals depends on how quickly the molten magma solidified. The more slowly the magma cools, the bigger the crystals.
3) Metamorphic rocks-Formation
They formed from other rocks that are changed because of heat or pressure.
Earth movements can cause rocks to be deeply buried or squeezed. As a result, the rocks are heated and put under great pressure. They do not melt, but the minerals they contain are changed chemically, forming metamorphic rocks.
Sometimes, metamorphic rocks are formed when rocks are close to some molten magma, and so get heated up.
Do rocks stay the same forever?
The Earth's rocks do not stay the same forever. They are continually changing because of processes such as weathering and large earth movements. The rocks are gradually recycled over millions of years. This is called the rock cycle.
For instance, sedimentary rocks can be changed into metamorphic rocks, and these can be weathered and the pieces transported away. These pieces could be deposited in lakes or seas and eventually form new sedimentary rock. Many routes through the rock cycle are possible.
This is what we call the Rock Cycle
What are rocks?
Rocks are made of grains that fit together. Each grain in the rock is made from a mineral, which is a chemical compound. The grains in a rock can be different colours, shapes and sizes.
Some types of rock have interlocking grains that fit tightly together. Granite is a rock with interlocking grains. Other types of rock have rounded grains. Sandstone is a rock with rounded grains.
How many types of Rocks are there?
There are three main types of rock: sedimentary, igneous and metamorphic.
1) Sedimentary Rocks-Formation
A river carries, or transports, pieces of broken rock as it flows along. When the river reaches a lake or the sea, its load of transported rocks settles to the bottom. We say that the rocks are deposited. The deposited rocks build up in layers, called sediments. This process is called sedimentation.
The weight of the sediments on top squashes the sediments at the bottom. This is called compaction. The water is squeezed out from between the pieces of rock and crystals of different salts form.
The crystals form a sort of glue that sticks or cements the pieces of rock together. This process is called cementation.
These processes eventually make a type of rock called sedimentary rock. It may take millions of years for sedimentary rocks to form.
Therefore, these are the different processes in order:
1) sedimentation → 2) compaction → 3) cementation
2) Igneous rocks-Formation
The inside of the Earth is very hot - hot enough to melt rocks. Molten (liquid) rock forms when rocks melt. The molten rock is called magma. When the magma cools and solidifies, a type of rock called igneous rock forms.
Igneous rocks contain randomly arranged interlocking crystals. The size of the crystals depends on how quickly the molten magma solidified. The more slowly the magma cools, the bigger the crystals.
3) Metamorphic rocks-Formation
They formed from other rocks that are changed because of heat or pressure.
Earth movements can cause rocks to be deeply buried or squeezed. As a result, the rocks are heated and put under great pressure. They do not melt, but the minerals they contain are changed chemically, forming metamorphic rocks.
Sometimes, metamorphic rocks are formed when rocks are close to some molten magma, and so get heated up.
Do rocks stay the same forever?
The Earth's rocks do not stay the same forever. They are continually changing because of processes such as weathering and large earth movements. The rocks are gradually recycled over millions of years. This is called the rock cycle.
For instance, sedimentary rocks can be changed into metamorphic rocks, and these can be weathered and the pieces transported away. These pieces could be deposited in lakes or seas and eventually form new sedimentary rock. Many routes through the rock cycle are possible.
This is what we call the Rock Cycle
WEATHERING
Do rocks wear away?
Yes, rocks gradually wear away. This is called weathering. There are three types of weathering:
▪ physical weathering
▪ chemical weathering
▪ biological weathering
What is physical weathering or freezing-thaw weathering?
Physical weathering is caused by physical changes such as changes in temperature, freezing and thawing, and the effects of wind, rain and waves.
Temperature changes
When a rock gets hot it expands a little, and when a rock gets cold it contracts a little. If a rock is heated and cooled many times, cracks form and pieces of rock fall away. This type of physical weathering happens a lot in deserts, because it is very hot during the day but very cold at night.
Wind, rain and waves
Wind, rain and waves can all cause weathering. The wind can blow tiny grains of sand against a rock. These wear the rock away and weather it. Rain and waves can also wear away rock over long periods of time.
Freeze-thaw
Water expands slightly when it freezes into ice. This is why water pipes sometimes burst in the winter. You might have seen a demonstration of this sort of thing at school - a jar filled to the brim with water eventually shatters after it is put into a freezer.
The formation of ice can also break rocks. If water gets into a crack in a rock and then freezes, it expands and pushes the crack further apart. When the ice melts later, water can get further into the crack. When the rock freezes again, it expands and makes the crack even bigger.
This process of freezing and thawing can continue until the crack becomes so big that a piece of rock falls off
Weathering
Biological weathering
Plants can cause biological weathering
Animals and plants can wear away rocks. This is called biological weathering. For example, burrowing animals such as rabbits can burrow into a crack in a rock, making it bigger and splitting the rock.
You may have seen weeds growing through cracks in the pavement. If you have gone for a walk in the countryside, you may even have seen bushes or trees growing from cracks in rocks or disused buildings. This is because plant roots can grow in cracks. As they grow bigger, the roots push open the cracks and make them wider and deeper. Eventually pieces of rock may fall away.
People can even cause biological weathering just by walking. Over time, paths in the countryside become damaged because of all the boots and shoes wearing them away.
Do rocks wear away?
Yes, rocks gradually wear away. This is called weathering. There are three types of weathering:
▪ physical weathering
▪ chemical weathering
▪ biological weathering
What is physical weathering or freezing-thaw weathering?
Physical weathering is caused by physical changes such as changes in temperature, freezing and thawing, and the effects of wind, rain and waves.
Temperature changes
When a rock gets hot it expands a little, and when a rock gets cold it contracts a little. If a rock is heated and cooled many times, cracks form and pieces of rock fall away. This type of physical weathering happens a lot in deserts, because it is very hot during the day but very cold at night.
Wind, rain and waves
Wind, rain and waves can all cause weathering. The wind can blow tiny grains of sand against a rock. These wear the rock away and weather it. Rain and waves can also wear away rock over long periods of time.
Freeze-thaw
Water expands slightly when it freezes into ice. This is why water pipes sometimes burst in the winter. You might have seen a demonstration of this sort of thing at school - a jar filled to the brim with water eventually shatters after it is put into a freezer.
The formation of ice can also break rocks. If water gets into a crack in a rock and then freezes, it expands and pushes the crack further apart. When the ice melts later, water can get further into the crack. When the rock freezes again, it expands and makes the crack even bigger.
This process of freezing and thawing can continue until the crack becomes so big that a piece of rock falls off
Weathering
Biological weathering
Plants can cause biological weathering
Animals and plants can wear away rocks. This is called biological weathering. For example, burrowing animals such as rabbits can burrow into a crack in a rock, making it bigger and splitting the rock.
You may have seen weeds growing through cracks in the pavement. If you have gone for a walk in the countryside, you may even have seen bushes or trees growing from cracks in rocks or disused buildings. This is because plant roots can grow in cracks. As they grow bigger, the roots push open the cracks and make them wider and deeper. Eventually pieces of rock may fall away.
People can even cause biological weathering just by walking. Over time, paths in the countryside become damaged because of all the boots and shoes wearing them away.
Weathering
Chemical weathering
Limestone cavern in the Peak District
The weathering of rocks by chemicals is called chemical weathering. Rainwater is naturally slightly acidic because carbon dioxide from the air dissolves in it. Minerals in rocks may react with the rainwater, causing the rock to be weathered.
Some types of rock are easily weathered by chemicals. For example, limestone and chalk are made of a mineral called calcium carbonate. When acidic rainwater falls on limestone or chalk, a chemical reaction happens. New soluble substances are formed in the reaction. These are washed away and the rock is weathered.
Gabbro, a hard wearing rock
Chemical weathering can hollow out caves form and make cliffs fall away.
Some types of rock are not easily weathered by chemicals. For example, granite and gabbro are hard rocks that are weathered only slowly. Still some of their minerals do react with the acids in rainwater to form new, weaker substances that crumble and fall away.
Acid rain
Statues damaged by acid rain
When fossil fuels such as coal, oil and natural gas are burned, carbon dioxide and sulphur dioxide escape into the air. These dissolve in the water in the clouds and make the rainwater more acidic than normal. When this happens, we call the rain 'acid rain'.
Acid rain makes chemical weathering happen more quickly. Buildings and statues made from rock are damaged as a result. This is worse when the rock is limestone rather than granite. Acid rain also kills trees and fish.
Chemical weathering
Limestone cavern in the Peak District
The weathering of rocks by chemicals is called chemical weathering. Rainwater is naturally slightly acidic because carbon dioxide from the air dissolves in it. Minerals in rocks may react with the rainwater, causing the rock to be weathered.
Some types of rock are easily weathered by chemicals. For example, limestone and chalk are made of a mineral called calcium carbonate. When acidic rainwater falls on limestone or chalk, a chemical reaction happens. New soluble substances are formed in the reaction. These are washed away and the rock is weathered.
Gabbro, a hard wearing rock
Chemical weathering can hollow out caves form and make cliffs fall away.
Some types of rock are not easily weathered by chemicals. For example, granite and gabbro are hard rocks that are weathered only slowly. Still some of their minerals do react with the acids in rainwater to form new, weaker substances that crumble and fall away.
Acid rain
Statues damaged by acid rain
When fossil fuels such as coal, oil and natural gas are burned, carbon dioxide and sulphur dioxide escape into the air. These dissolve in the water in the clouds and make the rainwater more acidic than normal. When this happens, we call the rain 'acid rain'.
Acid rain makes chemical weathering happen more quickly. Buildings and statues made from rock are damaged as a result. This is worse when the rock is limestone rather than granite. Acid rain also kills trees and fish.
Freeze-thaw weathering
It is made when:
-water gets in cracks at day
-then , at night, it turns into ice, expanding its volume, and making the rock bigger
-at day it turns into liquid and starts the process again.
It is made when:
-water gets in cracks at day
-then , at night, it turns into ice, expanding its volume, and making the rock bigger
-at day it turns into liquid and starts the process again.
Exfoliation weathering
Exfoliation is a type of weathering. it consists in the expansion and contraction of the rocks. This will eventually take the outer layer of the rock.
Sand blasting
Sand blasting is the last type of weathering I'm going to talk about. It consists in corroding a rock with wind. A rock will is corroded quicker if the wind has sand.
What is the difference between weathering and erosion?
Weathering is the wearing away of rocks while erosion is the movement of the broken pieces away from the site of weathering. Afterwards, transport occurs (either wind or rivers move the pieces).
In effect, rivers and streams can move pieces of rock. Fast flowing rivers can transport large rocks, but slow moving rivers can only transport tiny pieces of rock.
As the pieces of rock are carried along by the water, they bash against each other and the river bed. They gradually wear away because of this. They become smaller and more rounded.
Weathering is the wearing away of rocks while erosion is the movement of the broken pieces away from the site of weathering. Afterwards, transport occurs (either wind or rivers move the pieces).
In effect, rivers and streams can move pieces of rock. Fast flowing rivers can transport large rocks, but slow moving rivers can only transport tiny pieces of rock.
As the pieces of rock are carried along by the water, they bash against each other and the river bed. They gradually wear away because of this. They become smaller and more rounded.