Rocks

1. Rocks They are made in a variety of ways, but …

2. … most of them start out in the mantle And this is how they get out

3. Igneous rocks are formed when lava or magma cools down and solidifies If the lava or magma cools QUICKLY it has SMALL crystals If the lava or magma cools SLOWLY it has BIG crystals These rocks are Igneous rocks

4. Igneous rocks Obsidian Granite Which one has crystals you can see? How did it cool? Pumice

5. What are igneous rocks like? • When they were formed they were a liquid. • They were very hot rock that originally came from the magma at the centre of the earth. • Once they escaped from the mantle they began to cool • On the surface (where the liquid rock is called lava) they cool quickly and like toffee do not have crystals in it but they are very hard • If the magma pushed in between layers of other rocks, away from the surface, they cool slowly. • They contain crystals, very hard, never contain fossils (because there were no living things in the mantle)

6. Pressure from rocks above… …and heat from magma nearby Metamorphic rocks Metamorphic rocks are formed by the combined effect of heat and pressure on other rocks:

7. Quartzite Slate Marble Metamorphic rocks I was sand-stone I was limestone Did you know I was once clay?

8. What are metamorphic rocks like? • They were made from other rocks were acted on by heat and pressure over a long time • Sometimes have tiny crystals, no fossils because any remaining animal and plant bits would have been cooked in the process! • They always hard and sometimes arranged in layers

9. 2) Transportation 3) Deposition 4) Burial Sedimentary rocks How sedimentary rocks are formed: 1) Weathering and erosion

10. What is the difference between weathering and erosion? • Erosion is the wearing away of rock by wind, water or ice (which means also that is taken away too). We will come back to that another day! • Weathering is the breaking down of rock by weather, plants and animals (which means it tend to stay where it is) – a bit more about this in a minute.

11. Limestone Sandstone Conglomerate Sedimentary rocks

12. Sedimentary rocks are the only ones … • … that may have plant or animal remains trapped in them • Metamorphic and igneous rocks were too hot or too squashed to allow them to survive

13. More about weathering … • Physical weathering • (a) Freeze-thaw weathering • Water may enter cracks in rocks. • In areas where the temperature falls below the freezing point of water, the water will turn into ice when it is cold enough. • Water expands as it freezes. • The ice now exerts pressure on the walls of the crack, pushing them further apart and widening the crack. • Over time, the crack becomes wider and the rock may break apart.

14. More about weathering … • Physical weathering • (b) Onion-skin weathering • Large changes in temperature: • Changes in temperature cause the surface of the rock to expand and contract more than the interior of the rock. • This weakens the rock and causes cracks to form.

15. More about weathering … • Biological weathering • Plant roots and animal burrows can destabilise rocks. • Lichen that grows on rock surfaces gradually wears it away.

16. More about weathering … • Chemical weathering occurs when rocks are exposed to water. • Rainfall is naturally acidic due to the carbon dioxide dissolved in it. • Chemical reactions taking place between the water and the rock cause the rock to break down

17. Three types of rocks • Igneous: 65% • Metamorphic: 27% • Sedimentary: 8%

18. Summary

19. The rock cycle • The rock cycle describes the perpetual recycling of minerals by • weathering and erosion processes on the surface • transport and deposition processes involving water, ice, waves or wind • rock creation and transformation involving crust and tectonic processes • Landscape creation

20. The Rock Cycle

21. This is a bit easier to understand

22. Rocks revision quiz • What are the 3 types of rock? • What type of rock are the following: • Sandstone, limestone, granite, basalt, slate • What type of rock would a mountain probably be made out of? • What are the two conditions needed for a metamorphic rock toform? • Which metamorphic rock is formed from limestone? • Why wouldn’t you find any fossils in igneous or metamorphic rocks? • You find a rock containing crystals. What type of rock would it most probably be? • What is molten rock that is inside the Earth called? • What is molten rock that is outside the Earth (i.e. erupted) called?

23. Rocks revision quiz • Name one example of physical weathering. • Name one example of biological weathering. • Acid rain is an example of chemical weathering. What poisonous gas (given off by car exhausts and power stations) causes acid rain? • Granite is an igneous rock and contains large crystals. Did it cool down slowly or quickly? • In the rock cycle what causes igneous rock to become sedimentary rock? • In the rock cycle again what causes the sedimentary rock to become metamorphic rock? • Gravestones are usually made out of marble or granite instead of limestone or sandstone. Why? • A piece of rock contains layers. What type of rock would it probably be?