Rock Types & Formation

1. Rock Types & Formation 5th year Geography

2. 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.

3. Rocks • Rocks vary in their: • Origin • Formation • Characteristics

5. Rock Groups • Three major rock groups exist: • Igneous • Sedimentary • Metamorphic

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

7. 2 Types of Igneous Rock • Plutonic or intrusive rocks • Formed when lava cooled and solidified on the Earth’s surface or close to the surface • e.g. basalt • Volcanic and extrusive • Formed when magma cooled down and solidified inside the Earth’s crust • e.g. granite

8. 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

9. Granite

10. 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

12. Basalt

13. 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

15. Giants Causeway

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

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

19. 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

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

21. 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

22. Limestone

23. Sandstone • Inorganicsedimentary 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

24. Sandstone

26. Metamorphic Modified due to either great heat or pressure or both

27. 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

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

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

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

32. Croagh Patrick

33. 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)