Rock Types & Formation 5 th year Geography

Learning Outcome Identify the three main rock groups. Locate examples of each rock type on a map of Ireland. Understand the formation & main characteristics of two types of rock from each group. Answer an essay style exam question, explaining in detail the formation of one rock type.

Rocks Rocks vary in their:  Origin  Formation  Characteristics

Rock Groups Three major rock groups exist:  Igneous  Sedimentary  Metamorphic

Igneous 1.Magma rises, cools and solidifies to form igneous rocks 2.Magma reaches the surface, it forms volcanic rock 3.Magma cools and hardens within the crust, it forms plutonic rock

2 Types of Igneous Rock I.Plutonic or intrusive rocks  Formed when lava cooled and solidified on the Earth’s surface or close to the surface  e.g. basalt I.Volcanic and extrusive  Formed when magma cooled down and solidified inside the Earth’s crust  e.g. granite

Igneous rocks contain crystals  Size tells length of time it took rock to cool  Large crystals cooled slowly within the Earth’s crust  Small crystals, cooled quickly on the Earth’s surface

Granite

 Coarse-grained  Formed when magma cooled deep within the Earth’s crust  Contains minerals of feldspar, quartz and mica  Varies in colour – white, grey, pink or black  Crystals are large, the rock cooled slowly  e.g. Wicklow Mountains

Basalt

 Fine-to-medium- grained  Ranges in colour – black to dark grey  Formed when lava cooled quickly on the Earth’s surface  Small crystals  e.g. Antrim-Derry Plateau  Giant’s Causeway  Six-sided columns, hexagonal in shape

Giants Causeway

Sedimentary  Rock is destroyed where denudation occurs on the surface  Weathering  Erosion  Break down into sediments  Sediments are then deposited and compressed

Lithification A process where sediments compact under pressure and over time become solid rock. Eg; Loose particles of sand become sandstone.

Sedimentary rock  Formed over millions of years  Rock fragments and the remains of animals and plants compressed under pressure to form solid rock  e.g. limestone and sandstone

Two types of sedimentary rock I.Inorganic sedimentary rock  Inorganic sedimentary rock formed from the broken down remains of pre- existing rock I.Organic sedimentary rock  Organic sedimentary rock formed from the remains of animal and plant life

Limestone  Organic sedimentary rock  Most common type of rock in Ireland  Cemented and compressed remains of fish and other sea creatures  Over millions of years compressed and formed slowly into solid rock  Carboniferous period  Contains calcium carbonate  Varies in colour - greyish white, black, dark grey  e.g. the Burren in Co. Clare

Limestone

Sandstone  Inorganic sedimentary rock  Coarse  Usually brown or red  Formed approximately 400 million years ago  Sediments laid down in layers  Each successive layer compressed the next layer  Cemented to form sandstone  e.g. Comeragh Mountains, Co. Waterford

Sandstone

Metamorphic Modified due to either great heat or pressure or both

Metamorphic Rock  Sedimentary or igneous rocks changed by either great heat or pressure (or both)  Formation can depend on;  Magma  Folding  Appearance, texture and chemical composition change

Types of metamorphism i. Thermal  heat from magma  rocks change in composition ii. Regional  great heat and pressure over a large area  fold mountain  colliding plates  rising magma

Marble  Metamorphic rock  Limestone  Heat and pressure  Various colours  Connemara (green)  Kilkenny (black)  Cork (red)  Rathlin Island, Antrim and Carrara, Italy (white)

Quartzite  Metamorphic  Sandstone  Heat and pressure  Mountain building  Sandstone came into contact with magma  Light-coloured rock, e.g. Croagh Patrick, Co. Mayo

Croagh Patrick

Exam Question Name one type of igneous / sedimentary rock. Name one Irish location where this type of rock was formed and explain in detail how it was formed. (30m)