Formation and characteristics of rock types![]() Rocks are classified into three types depending on how they are formed. They are igneous, sedimentary and metamorphic. Igneous Igneous rocks are formed when magma from the mantle cools and hardens. If it cools underground, it is intrusive. This cools slowly and forms large crystals and a coarse texture. If it cools above ground after a volcanic eruption, it is extrusive. This cools quickly and forms fine crystals and a fine texture. Igneous rock can form a batholith, a dome of rock formed by large dome of magma cooling. Igneous rocks are tough and resistant to erosion. Example of igneous rocks in the UK are granite and basalt. Sedimentary As the name suggests, these rocks are formed when layers of sediment at the bottom of a sea or lake are compacted. This process is called lithification. The sediment comes from the shells and skeletons of dead sea creatures, as well as eroded material from rocks. Although some sedimentary rocks are tough, such as limestone, most are weaker than igneous and metamorphic rocks. Sedimentary rocks often contain fossils and UK examples include limestone, chalk, clay and shale. Metamorphic Metamorphic rocks are rocks that have “morphed” due to heat and pressure: Rocks deep in the Earth are changed by the pressure on them. Tectonic plate collisions create heat and pressure which changes the rocks. Heat from magma causes rocks to change The rock becomes harder and more compact after the change, so more resistant to erosion. For example, limestone becomes marble and clay becomes slate. The formation of all these rock types is linked by the rock cycle (see left). Distribution of rock types![]() The map below shows the distribution and ages of rock across the UK. Here we can see the upland-lowland differences in geology. The lowland south and east is made up of much more recent sedimentary rocks, whereas as the upland areas in Scotland, Wales and northern England are dominated by older sedimentary rocks, and metamorphic and igneous rocks which are more resistant to erosion. These different rock types have shaped the landscape of the UK not just through the physical features they form, but through the impact they have had on how humans use the land and how that in turn changes the landscape. Sources: The Geological Society. (no date) Rock Cycle Processes. [Accessed on 05/08/15] Available from: http://www.geolsoc.org.uk/ks3/gsl/education/resources/rockcycle/page3446.html Coordination Group Publications Ltd. (CGP) (2010) GCSE Geography: The Revision Guide. CGP.
0 Comments
|
AuthorMy name is Heather and I am going to begin my SCITT course to train as a Geography teacher. ArchivesCategories
All
|