Rocks Geography Notes JC-Learn. JC-Learn. Geography Notes Rocks. 1 P a g e

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Ferdinand Reynolds
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1 JC-Learn Geography Notes Rocks 1 P a g e

2 Rocks The crust of the earth is made up of rocks. Three major rock groups exist, and they are formed in different ways: Group Igneous Sedimentary Metamorphic How rock was formed When magma cooled down and solidified Compressed remains of sea creatures and animals, plants and rock fragments When sedimentary/ igneous rocks are altered by high temperatures or pressure, or both Examples Granite Basalt Limestone Sandstone Coal Shale Marble Quartzite Location Wicklow Mountains Giant s Causeway (Antrim) The Burren (Clare) Arigna (Roscommon) Connemara Croagh Patrick (Mayo) Igneous Rocks Igneous rocks were formed when magma cooled down and then solidified. The two most common igneous rocks are basalt and granite. Basalt Basalt is a fine to medium-grained igneous rock. It ranges in colour from black to dark grey. It formed when lava cooled on the earth s 2 P a g e

Here, the lava cooled, contracted and eventually cracked to form six-sided columns.

3 surface. There are tiny crystals in this rock, because the lava cooled very quickly. It is found in the Antrim-Derry Plateau, which includes the Giant s Causeway (picture below). Here, the lava cooled, contracted and eventually cracked to form six-sided columns. Granite This is a course-grained rock (in picture below), which varies in colour (white, grey, pink/ black). It formed when magma cooled deep within the earth s crust, and it has large crystals as the magma cooled slowly. It is often used for kitchen worktops. Granite is found in the Wicklow Mountains. 3 P a g e

Sedimentary Rocks Sedimentary rocks were formed over millions of years and resulted when rock fragments and the remains of animals and plants built up and were compressed under pressure to form solid

4 Sedimentary Rocks Sedimentary rocks were formed over millions of years and resulted when rock fragments and the remains of animals and plants built up and were compressed under pressure to form solid rock. Limestone This is the most common rock type in Ireland. The Burren, in Clare (picture below), is a well-know limestone region (karst region). It is made from the compressed remains of fish and other sea creatures, built up on top of each other. Fossils are often found in limestone. It can vary in colour from greyish white to black and dark grey. It is laid down in horizontal layers called strata Bedding planes are the divisions between the layers Vertical cracks (joints) can occur in limestone It is permeable (allows water through) It is easily weathered, which means it is easily worn down It is widely used to make cement for building trade (eg. GPO) Sandstone This was formed when sand was worn away from the earth s crust and transported by wind and rivers. The grains of white sand were deposited on beds of lakes and seas as well as in deserts. Layers built up and compressed to form sandstone. It is a coarse, brown/red rock Found in the Comeragh Mountains 4 P a g e

5 Metamorphic Rocks Metamorphic rocks are formed when either sedimentary or igneous rocks are changed by high temperatures or pressure, or both. Great heat - magma forced into area of the earth s crust, it heats surrounding rock, changing its composition to form metamorphic rock Great pressure - plates colliding builds up pressure in crust, which causes rock to change into metamorphic rocks Marble Marble is a metamorphic rock formed by heat or pressure on limestone. It is a hard, crystalline rock, which can be found in Connemara (green marble). It can be used for kitchen worktops and fireplaces Quartzite This was once sandstone, but was changed due to either great heat or pressure. It is a light-coloured rock, which is found in Croagh Patrick (Mayo). Extracting Rock from Earth Rocks provide us with important resources, such as energy and building materials. Energy Examples of rock-based energy resources include coal, oil and gas. These energy sources are all fossil fuels. They are extracted from earth s crust in different ways: Coal is extracted by shaft mining - as coal lies seams deep beneath earth s surface. Vertical shafts are made to reach the seams. Oil and gas are drilled and pumped to the surface. Where oil and gas are found under the seabed, offshore drilling occurs. Drilling is carried out from a rig and the oil/gas is pumped inland by a pipeline. 5 P a g e

6 Building materials Examples of rock-based building materials include: Stone Gravel Sand These resources are used for building materials. They lie on/ close to the surface. Quarrying is used to extract these rocks. Some people oppose it as it is noisy and an eyesore, but it also has benefits, like providing employment. 6 P a g e

Angel International School - Manipay 1 st Term Examination November, 2015

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