A Closer Look At Rocks

Do you remember the names of the 3 rock families?

That’s Right!

Igneous

Sedimentary

Metamorphic

Let’s Take a Closer Look at Igneous Rocks!

These rocks are formed from either magma or lava

Intrusive igneous rock are formed inside the Earth from magma

– Usually take a long time to cool and have large crystals

Extrusive igneous rock is formed on the Earth’s surface from lava

– Take a shorter time to cool and have small crystals

Igneous rocks are usually the hardest type of rock and last longer than any other type of rock

Sedimentary Rocks

These rocks are formed from sediment

– Rock particles, decaying animals, plants and minerals

– Layers can be made on land or in water

Particles are moved around by water, wind and ice

Forming Loose Sediment into Rock

Rock particles get pressed together forming layers that make up sedimentary rock

Some small particles may be formed into rock by pressure alone examples silt and clay

In some sedimentary rocks the particles are held together by minerals that have crystallized acting as a cement

Metamorphic Rock

Heat and Pressure Change Rocks

When a rock changes by heat and or pressure it undergoes metamorphism

– The original igneous or sedimentary rock is called the parent rock

– It changes into a metamorphic rock

A metamorphic rock can also be a parent rock

– It changes into another metamorphic rock

Metamorphism

Pressure causes the minerals to flatten out

It remains as a solid

Rocks DO NOT MELT when they undergo metamorphism

Recrystallization

Heat and pressure break bonds. Then the atoms rejoin in a new way and form new bonds

Crystals can become larger as more atoms join the crystal structure

Atoms can combine in a different way and new minerals can be formed.

Metamorphic Rocks Develop Bands of Minerals

Foliation – Arrangement of minerals in flat or wavy parallel

bands

Foliated rocks – Foliation occurs when a rock is under pressure

– This develops when minerals flatten out

Non-foliated rocks – May not display foliation because it is made up of

one mineral

– Example – marble

– It may not have been subjected to high pressure