Igneous and Metamorphic rock essay

Granite description

Course grained and multi coloured rock. It is a plutonic rock which means it cools slowly beneath the surface.

Granite formed in 2 ways

Either a folding at a convergent plate boundary or when an oceanic plate subducts under a continental plate.

2nd way explanation

The subducting plate melts allowing magma to rise into the overlying plate through sedimentary rock.

2nd way continued explanation - insulation

The magma cools slowly over millions of years to form granite. It cools slowly due to the surrounding layers of sedimentary rock acting as an insulator.

cooked sedimentary

Sometimes the surrounding sedimentary rock can be cooked by the heat and turned into metamorphic rock. This acts as a cao of resistant rock which protects the granite from weathering.

Example

The Leinster batholith cover 1500km of land and was created 400 million years ago when NA and EU plates collided.

Marble

Marble is a metamorphic rock that is formed when limestone is subject to immense heat and pressure.

Regional metamorphism

Occurs at plate boundaries when the friction is so strong it causes intense heat. This leads to wide scale metamorphism.

Heat and minerals

The heat causes minerals in limestone to melt and a non foliated rock is formed. The heat causes the minerals to expand and become big crystals.

Colour of marble

Varies greatly on the purity of the marble. Pure white is found in rathlin and black is found in kilkenny due to the high amount of carbon.