Rocks and how they are formed...

Topic 2

Sedimentary Rocks

Rivers carry rocks along as they travels. As rocks are travelling, they often get broken down by other materials (This process it call erosion). When the river reaches a sea, the travelling rocks are deposited at the bottom of the sea/lake. These get built up in to layers, called Sediments. The weight of the sediments grow larger and eventually compacts the layers together, causing the water to be squeezed out. This makes crystals of different salts form.

The different processes of sedimentary rocks being formed are:

Sedimentation - Where deposited rocks build up into layers called sediments.

Compaction- Where the layers of rock are compacted together into rocks

Cementation- Where the crystals form a glue that stick the pieces of rock together

The order of these processes goes: Sedimentation-Compaction-Cementation

Igneous Rocks.....

Igneous rocks are rocks that are formed by lava or magma. These are mainly formed by volcanoes or other natural disasters that cause a change of temperature in the earths' crust. Igneous rocks can be formed above ground or underground. The majority of igneous rocks are formed underground. Underground, these are formed when magma deep in the earth gets trapped in small pockets. As these pockets of magma cools slowly underground, they become igneous rocks. Igneous rocks are also formed when volcanoes erupt causing the magma to rise above the earths surface. Igneous rocks are formed as the lava cools above land.

Some examples of common igneous rocks are:






Metamorphic rocks....

Metamorphic rocks are rocks that have been subjected to tremendous pressure or heat, or a combination of both. These conditions cause the minerals inside the rock to become unstable and rearrange into a more stable formation. This heat causes them to change into a different type of rock. Metamorphic rocks are usually resistant to erosion and weathering, This makes them quite hard-wearing, which is good for sculpting solid objects. The word 'Metamorphic' comes from the Greek terms 'Change' and 'Form'. Metamorphic rocks begin changing at temperatures from 100-700 degrees celsius. There are many different characteristics of metamorphic rocks. Some of these include- Layers of visible crystals, mineral crystals of different sizes, Rarely has pores or openings, may only be composed of one mineral, e.g marble, quartzite...


Erosion is when rocks (or other things like land) are broken down. Sedimentary rocks are more likely to be broken down by erosion as metamorphic rocks and igneous rocks all have interlocking crystals, and sedimentary rocks don't. This means that sedimentary rocks aren't as tough as other rocks and therefore are more easily eroded.