Geography GCSE Unit (1)

Igneous - formed by the cooling of molten magma underground or on the ground by volcanic activity. Igneous rocks are made of interlocking crystals. They are touch rocks and are resistant to erosion. Basalt, Granite.

Sedimentary - formed by the compaction & cementation of sediments; usually deposited in the sea, it also includes organic material. Sedimentary rocks usually form layers called beds. They often contain fossils. Although some sedimentary rocks can be tough (limestone), most are weaker than igneous and metamorphic rocks. Sandstone, Limestone, Shale, Clay, Mudstone.

Metamorphic - formed by the alteration of pre-existing igneous, metamorphic or sedimentary rocks by heat/pressure. metamorphic rocks are crystalline. They often show layering called cleavage and banding. Metamorphic rocks tend to be very tough and resistant to erosion. Slate, Gniess.

Weathering is the disintigration or decay of rocks in their original place at, or close to the ground surface. it is largely caused by weather such as rainfall and changes in temperature.

Mechanical Weathering - also known as Physical Weathering, this involves the disintergration of rocks without any chemical changes taking place. It often results in piles of angular rock fragments called scree found at the foot of bare rocky outcrops. Freeze-thaw.

Chemical Weathering - in the UK, a chemical change occurs when weathering takes place. rainwater, being slightly acidic, can slowly dissolve certain rocks and minerals. Those minerals and particles unaffected by chemical weathering are usually left behind to a form a fine clay deposit.

Biological Weathering - this involves the actions of flora and fauna. Plant roots are affective at growing and expanding in cracks in the rocks. Rabbits can be effective in burrowing into weak rocks such as sands.