WHAT ARE ROCKS?

Types of rocks

The 3 types are: Igneous Sedimentary Metamorphic

Igneous rocks Igneous rocks are formed from molten

rock called magma. They are mostly crystalline (made up of interlocking crystals) and usually very hard to break. E.g. granite, basalt, andesite.

GraniteBasalt

The formation of igneous rocks

magma

Sed

imen

t ary

rock

s

volcanoExtrusiveigneous rocks arecooled quicklyso small crystals form (e.g. basalt).

Intrusiveigneous rocks are cooled more slowly so large crystals form (e.g. granite).

Basalt pillars

These pillars were formed when lava cooled on the Earth’s surface.

Sedimentary Sedimentary rocks are formed from

sediment grains deposited by water, wind or ice. They are always formed in layers, called “beds” or “strata”, and quite often contain fossils. E.g…

Sandstone Limestone Chalk

The formation of sedimentary rocks

These were formed from layers of sediment which were squeezed together.

newdeposits

layers ofsedimentsgettingolder

sea/lake/riverland

rivers

Metamorphic Metamorphic rocks were once igneous

or sedimentary rocks, but have been changed (metamorphosed) as a result of intense heat and/or pressure within the Earth’s crust. E.g…

Slate Marble Gneiss, pronounced ‘nice’

Metamorphic rocks are formed by the effect of extreme pressures and temperatures deep within the Earth.

This alters the structure of the existing rock.

Metamorphic rock - formation

The formation of metamorphic rocks

magma

Sed

imen

t ary

rock

s

sedimentaryrocksare changedhere due toheat and pressure.

volcano

Continent collision causes metamorphism and huge folds like this one in Scotland.

Metamorphic rocks

Rock type Definition Formation ExampleIgneous Rocks formed of

interlocking crystals. Tough, hard and resistant to erosion

Formed by the cooling of molten magma either underground (intrusive) or on the ground (extrusive) due to volcanoes

Basalt, granite

Sedimentary Formed in layers called strata. Often contain fossils. Some are tough and others are weaker than igneous or metamorphic rocks

Formed by the compaction of sediments, usually deposited by the sea.

Sandstone, limestone, shale, clay

Metamorphic Also formed of interlocking crystals. Very tough and resistant to erosion

Formed by heat and/or pressure changing existing sedimentary or igneous rocks to metamorphic rocks

Slate, marble

sea

volcano

rocks are brokenup by the action

of weather

magma

slowsolidification

high pressureand temperature

transportationand deposition

rises to surfacewhere it

cools rapidly

melt

rocks riseto surface by

uplift and erosion

Igneous rocksbasalt

Igneous rocksgranites

magmaMetamorphic rocks slate and marble

Sedimentary rocksmudstone

sea

volcano

Igneous rocksbasalt

Igneous rocksgranites

rocks riseto surface by

uplift and erosion

rocks are brokenup by the action

of weather

magma

Metamorphic rocks slate and marble

Sedimentary rocksmudstone

slowsolidification

high pressureand temperature

transportationand deposition

rises to surfacewhere it

cools rapidly

melt

Homework:

Task – imagine you are a rock, describe your journey through the rock cycle.

Things to include: Are you an igneous, metamorphic or

sedimentary rock? What type of rock are you e.g. granite,

limestone.