Types of rocks and their distribution within the UK

These cards look at the characteristics, formation and distribution of igneous, sedimentary and metamorphic rocks.

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Igneous rocks

Brief definition: Rocks which are "formed by fire" i.e. by cooling lava or following the heat of a volcanic eruption

Where they were formed:

  • Underground below volcanoes where pressure is greater allowing other rocks to intrude
  • OR On the earth's surface after the volcanic eruption

How they were formed:

  • Lava cooling on the Earth's surface after being ejected during a volcanic eruption.
  • OR Magma cooling below the surface and intrusion by other rocks without reaching the surface.
  • OR Lava flowing from constructive margins or shield volcanoes cooling to form basalt rock

Rock types found in UK: Granite, Basalt, Obsidian, Pumice

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Sedimentary rocks

Brief definition: Rocks formed by collection of small rock fragments as well as plant and/or animal matter (known as sediments) creating layers.

Where they were formed: The sea bed where fragments have been transported separately by wind, ice and finally water, bringing them to the shore.

How they were formed:

  • The weight of the materials above compresses sediments (small rock fragments) downwards to form the rock, with the different fragments creating layers, with separating lines created by 'weakness' or bedding areas.
  • Also the remains of plants and animals.

Rock types found in UK: Sandstone, Clay, Limestone, Chalk, Calcium Carbonate, Coal, Flint, Shale, Mudstone

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Metamorphic rocks

Brief definition: Rocks which have been changed in either shape and/or form, beginning as either igneous or sedimentary but being changed by the elements.

Where they were formed: Along destructive tectonic plate boundaries and fault lines, where pressure and heat are higher.

How they were formed:

  • Starting as igneous/sedimentary rocks, heat and pressure cause physical and chemical reactions, changing the properties of the rock
  • (metamorphic derived from metamorphism - change in form)
  • Through the intrusion of magma
  • Dipping below the surface at tectonic boundaries

Rock types found in UK: Marble, Slate, Talc Carbonate, Talc Soapstone, Clay

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