Rocks are divided into three main groups based on how they are formed: igneous, sedimentary, and metamorphic. Igneous rocks form from cooled magma, sedimentary rocks form from compressed plant and rock remains, and metamorphic rocks form from rocks subjected to heat or pressure. Granite forms from slowly cooled magma and basalt forms from quickly cooled magma. Sandstone forms from compressed sand layers and limestone forms from compressed sea creature remains. Quartzite forms from metamorphosed sandstone and marble forms from metamorphosed limestone. Rocks are extracted through drilling, shaft mining, or quarrying.

1. Rocks
Rocks
Group How Formed
Igneous Cooled down Magma
Sedimentary Pressed remains of plants and other rocks
Metamorphic
Rocks that have been through a ‘Great
Change’ of heat or pressure
Igneous Rocks
Igneous rocks are formed from cooled down magma. Whether the magma cooled
down quickly or slowly determines the rock type formed.
Granite
Granite is a hard rock with crystals in it. It was formed when magma cooled slowly. It
is hard. It can be multi-coloured. It is used for kitchen worktops and fireplaces. It can
be found in the Wicklow Mts.
Basalt

2. Basalt is a heavy, black rock. It was formed when magma cooled quickly on the
earth’s surface. It is hard. It can be used for road surfaces. It can be found at the
Giant’s Causeway.
Sedimentary
Sedimentary rocks get their name from the build up of layers, called strata.
Sandstone
Sandstone is a soft rock. It varies in colour from yellow to dark brown in colour. It
was formed when layers of sand built up in layers. The sand is squeezed
(Compressed) together to form a rock. Used for ornamental building and stone walls.
Found in the mountains of Munster.

3. Limestone
Limestone is Ireland’s most common rock. It is soft and Grey in colour. It was
formed by the remains of dead sea creatures building up in layers on sea beds. The
layers are known as Bedding planes, these are separated by joints. It may contain
fossils. It is Permeable (water can pass through it) and easily worn by acid rain. It can
be found in the Burren in Co. Clare. Used for building up roads and for making
cement.
Metamorphic Rocks
The word Metamorphic means great change. Some rocks are subjected to either a
great deal of heat or pressure. This can cause them to change.

4. Quartzite
Sandstone changes to quartzite. It is very hard. Sometimes used for roads, Quartz is
used in watches. Found in Co. Donegal.
Marble
Marble used to be Limestone. It is also very hard. It has many uses because of its
beauty. Fireplaces, trophies etc. It can be found in many colours. Found in
Connemara and Kilkenny.
How Rocks are Formed Video
Extracting Rocks
Several methods are used to take rocks out of the ground.
 Drilling
 Shaft Mining
 Quarrying
Drilling

5. This is used to get oil and gas from deep under the earth’s surface. A deep hole is
drilled to get to the oil and it is then pumped to the surface.
Shaft Mining
This method is used for rocks under the surface of the earth E.g. Coal or Gold. A
vertical shaft is dug and then horizontal shafts dug across to the rock.
Quarrying
Most common form. Used for rock that is on the surface. Explosives are used to
break it up then lorries take it away.