Types of Rock
Geography: KS3, topic 7.1.2
The Three Main Types of Rock
There are three main types of rock on Earth. These are igneous, metamorphic and sedimentary rocks. Each of these rock types form under different conditions and as a result, have different properties.
Igneous rock
- Deep within the structure of the earth is molten rock called magma.
- Molten means it is ‘flowing’ rock- it is melted.
- The igneous rocks in the UK are from millions of years ago when the UK was close to a plate boundary.
- When the lava erupted out of the volcanoes, it cooled and solidified to form igneous rocks.
Igneous rock cont.
- Igneous rocks are mostly crystalline and contain interlocking crystals.
- These interlocking crystals make them very hard to break.
- The slower the magma cools, the larger the crystals in igneous rocks.
- Some examples of igneous rock are:
- Basalt
- Granite
Metamorphic rock
- Metamorphic rocks form from igneous or sedimentary rocks.
- So, if an igneous or sedimentary rock is placed under intense heat or pressure within the Earth, it becomes a metamorphic rock.
- Metamorphic rocks are crystalline and, because they form under high pressure, often have a ‘squashed’ look about them.
- Slate is the best known example of metamorphic rock.
Sedimentary rock
- Sedimentary rocks are formed as sediment builds up over time into layers.
- The layers can also be called strata.
- Because they build up through deposits of material from water, wind or ice, they often contain fossils.
- Some examples of sedimentary rocks are limestone and chalk.
Test yourself on Types of Rock
Which is NOT a main type of rock found on Earth?
Which type of rock can contain fossils?
Granite is an example of which type of rock?