Term 3 Rocks D2

Question 1

Explain the processes involved in formation of the different rock types (the rock cycle) (weathering, erosion, deposition, melting, crystallisation, compaction and cementation).

Answer 1

Weathering is where rocks are broken down into small pieces which are then eroded, transported from one place to another where they are deposited forming sediment. The sediment is then compacted and cemented forming sedimentary rock. This rock can be melted forming magma which may then crystalise forming igneous rock or it is exposed to intense heat / pressure, undergoing metamorphosis to form metamorphic rock.

Question 2

Explain the difference between (contrast) dynamic, regional and contact metamorphism

Answer 2

Metamorphic rock forms when igneous or sedimentary rock are altered by high temperature and pressure. Dynamic metamorphism is where the rock is altered mostly by pressure (crust scrapes past each other whilst contact metamorphism is where the rock is altered mostly by heat (magma intruding into rock). Regional metamorphism is where the rock is altered by heat and pressure (as plates collide or are buried).

Question 3

Explain why not all living things form fossils

Answer 3

For fossils to form the plant / animal remains need to be rapidly covered by sediment removing the O2 so that it does not decompose, these conditions best occur under water. It is no common for fossils to be preserved quickly. Hard body parts fossilise easily. Soft bodied organisms do not fossilise as they decompose rapidly but they can leave an imprint fossil.

Question 4

Explain the difference between physical, chemical & biological weathering

Answer 4

chemical – chemicals in the air, water and soil reacting with minerals in the rock (CO2, O2
physical – wind, temperature change, ice & water, crystallisation of salts

Question 5

Explain the difference between chemical, clastic and biogenic sedimentary rocks

Answer 5

Chemical sedimentary rock forms when minerals dissolved in ground water crystallise within the sediments or the water evaporates leaving behind the crystals which are interlocking.
Clastic sedimentary rock is formed from weathered rock and contains clasts (pieces if rock) and so no interlocking grains.
Biogenic: form when organic matter (dead plant and animals) and minerals made by living organsims such as coral, accumulate and are cemented together.

Question 6

Explain the difference between intrusive and extrusive igneous rocks

Answer 6

Intrusive igneous rocks form below the surface as magma cools very slowly forming large crystals, whereas extrusive igneous rocks form above the surface as lava cools rapidly forming very small crystals or no crystals