THE ROCK CYCLE

 Doc Brown's Chemistry - Earth Science & Geology Revision Notes

for KS4 Science, GCSE, IGCSE & O Level Courses

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All my GCSE/IGCSE level chemistry revision notes

2. The ROCK CYCLE explained - the relationship between igneous, metamorphic and sedimentary rocks

This pages summarises the connection between the different types of rock and how they are formed. Parts 3. to 9. expand on this theme with detailed notes on all the geological processes occurring.

2. The Rock Cycle - A 1st "Big Picture" View

Many of the features of the rock cycle are illustrated below in Fig 1. The Rock cycle. (see also Fig 2. below)

Fig 1. Summary of the features of THE ROCK CYCLE

The 'Rock Cycle' summarises the formation and relationship between the three types of rock, namely, igneous, metamorphic and sedimentary

Fig 2. The complexity of igneous and metamorphic rock formation

Sections 3. to 9. take you through all the details.

Rocks are classified into groups of IGNEOUS, METAMORPHIC and SEDIMENTARY ROCKS depending on their origin.

• All rocks have crystalline structure based on giant ionic or covalent structures (Chemical Bonding Notes)
• Physically they are relatively insoluble in water, poor heat and electrical conductors and have high melting points. They are generally hard materials but with quite some variation between rock types e.g. softer limestone (easily weathered) and much harder basalt rocks used for street cobbles.
• Generally speaking, igneous rocks like granite and basalt are much harder and 'weather resistant' than sedimentary rocks like limestone, shale and sandstone which erode much more easily. Rock type details are given in 4. to 6. below.
• The three generalised type of rock are discussed in detail in sections 4. to 6.
  • Section 4. Igneous rocks are formed from cooled molten magma or lava from the Earth's mantle below the crust.
  • Section 5. Sedimentary rocks are formed deep in the Earth's crust from highly compressed deposits of weathered rock material or mineral deposits from plants and animals.
  • Section 6. Metamorphic rocks are formed from re-existing sedimentary or igneous rocks by the action of heat and pressure deep underground in the Earth's crust.

Below is a simpler approach to the "THE ROCK CYCLE" to show the relationship between the three types of rocks

Fig 3. A simplified version of the ROCK CYCLE

Fig 4. An alternative detailed version of the ROCK CYCLE

[x] try to match up with the notes below

By the end you should be able to identify, describe and understand the processes shown in the diagram.

[e] - after erosion [g], transportation by eg water at [f], sedimentation [h], the sediments are buried by successive layers under pressure to cause cementation at [e], so sedimentary rock is formed eg sandstone

[f] - after erosion [g], transportation by eg water at [f], sedimentation [h], the sediments are buried by successive layers under pressure to cause cementation at [e], so sedimentary rock is formed

[g] - weathering and erosion occur more readily in mountainous areas [g], followed by transportation [f], sedimentation [h], cementation at [e] to form sedimentary rocks

[h] - weathering and erosion occur more readily in mountainous areas [g], followed by transportation by water usually [f], sedimentation [h], cementation at [e] to form sedimentary rocks

[k] - magma rises from the mantle at [n] and pours out in volcanic activity on land (and under the sea), this causes rapid cooling at [k] and igneous rocks of small crystals like basalt are formed

[l] - magma rises from the mantle at [n] and if it slowly crystallises at [l] and forms igneous rocks with large crystals like granite

[m] - deep lying rocks are under pressure or heated near the mantle can recrystallised to form metamorphic rocks at [m]

[n] is where magma rises from the mantle (may pour out as lava at [k]) or deep lying rocks get heated and melt into the mantle (destroying any fossils - not found in igneous rocks!, can also be destroyed at [m]

 Its a 'balanced' global cycle both internally and externally! Mountain ranges get pushed up, continents form, then the crust gets subducted and if not subducted, mountain ranges still get worn away by weathering and erosion ...

.... so everything gets recycled in the end!

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• NOTES Cue, QUIZ and WORKSHEET QUESTION LINKS

• INDEX OF EARTH SCIENCE PAGES

• foundation-easier multiple choice quiz on Earth Science

• higher-harder multiple choice quiz on Earth Science

•  Five Earth Science word-fill worksheets Q1 * Q2 * Q3 * Q4 * Q5

• Answers to the five GCSE Earth Science worksheets listed above

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