Rocks and Weathering

 The 3 types of rocks are:

-metamorphic

-sedimentary

-igneous

otherwise known as:

-changed rock

-sandstone

-fire stone

For example 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.

For example 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.

          The Rock Cycle

Sedimentation creates layers or rock particles

Compaction and cementation presses the layers and sticks the particles together. This creates sedimentary rock.

Rocks underground that get heated and put under pressure are changed into metamorphic rock.

Rocks underground that get heated so much they melt turn into magma. Magma is liquid rock. Magma also comes from deeper inside the Earth, from an region called the mantle.

• Pressure can force magma out of the ground. This creates a volcano. When the magma cools it turns into solid rock, called extrusive igneous rock.

• Magma that cools underground forms solid rock called intrusive igneous rock.

Areas of rock can move slowly upwards, pushed up by pressure of the rocks forming underneath. This is called uplift.

Weathering breaks down rocks on the surface of the Earth. There are three types of weathering - physical, chemical and biological.

Wind and water move the broken rock particles away. This is called erosion.

Rivers and streams transport rock particles to other places.

Rock particles are deposited in lakes and seas, where they build up to form layers. This starts the process of sedimentation which will create sedimentary rock.

Rocks with rounded grains are more likely to absorb water than rocks with interlocking grains.

 Rocks that absorb water are called porous.

Sedimentary Rock Cycle

The river transports bits of rock, and deposits them on the bottom of the river bed.

Deposited rocks build up in layers, and the weight of the top layers compresses the bottom layers

Deposited rocks build up in layers, and the weight of the top layers compresses the bottom layers

The compression squeezes out water, leaving salt crystals that cement the rocks together.

The compression squeezes out water, leaving salt crystals that cement the rocks together.  

Igneous Rock Cycle

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.

If the magma cools quickly, small crystals form in the rock. This can happen if the magma erupts from a volcano.This is called extrusive igneous rocks because they form from eruptions of magma.

If the magma cools slowly, large crystals form in the rock. This can happen if the magma cools deep underground. This is called intrusive igneous rocks because they form from magma underground.

Metamorphic Rock Cycle

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.

When a metamorphic rock is formed under pressure, its crystals become arranged in layers.

When a metamorphic rock is formed under pressure, its crystals become arranged in layers.

Metamorphic rocks sometimes contain fossils if they were formed from a sedimentary rock, but the fossils are usually squashed out of shape.

Metamorphic rocks can be formed from any other type of rock - sedimentary or igneous.

Weathering

Weathering

Weathering

Rocks gradually wear away. This is called weathering. There are three types of weathering:

• physical weathering

• chemical weathering

• biological 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. 

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.

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

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.

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.Chemical weathering can hollow out caves form and make cliffs fall away.

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'.

Weathering is the wearing away of rocks.

Erosion is the movement of the broken pieces away from the site of weathering.

Erosion happens when these pieces of rock fall away down the cliff.

In the photograph you can see a basalt cliff. At the bottom there are heaps of rocks, caused by weathering then erosion

Rivers and streams can move pieces of rock. This is called transport. 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.

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.

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