Page 244 - Big Ideas Year 10 sciPAD 2025

PHOTOCOPYING PROHIBITED
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244 SCIPAD - BIG IDEAS - BOOK 2
EARTH SYSTEMS
Types of Rock
Rocks are classified into three major types according to how they were formed:
Igneous Rocks
Igneous rocks are formed from
magma. The magma is forced up into,
and sometimes out of, the Earth’s crust.
As it cools, crystals begin to form and
the magma solidifies. The size of the
crystals depends on how quickly the
magma cools. Basalt contains small
crystals because it is formed from lava
which cools rapidly on the surface.
Granite contains large crystals as it is
formed by slow cooling inside the crust.
Other examples of igneous rocks
include scoria, pumice, obsidian and
ignimbrite.
Sedimentary Rocks
Sedimentary rocks form from grains of
eroded rock or undecomposed parts
of plants or animals. These sediments
settle in layers, usually under water. As
layers of sediment build up, older layers
become buried under newer layers
and their weight squeezes out water.
The sediment becomes cemented
together to form sedimentary rocks.
This process takes place over millions
of years.
For example, sand is compressed into
sandstone, mud is compressed into
shale and the remains of tiny shellfish
into chalk or limestone.
Metamorphic Rocks
When sedimentary rocks become
buried deep in the Earth’s crust they
are subjected to high temperature
and pressure. Over millions of years
this causes structural and chemical
changes (without melting) forming
metamorphic rocks. The immense
pressure of the weight of rock above
causes crystals to form in parallel
planes or bands.
For example, shale is changed into
the metamorphic rocks slate, chalk to
marble, and sandstone to quartzite.
Pounamu is probably New Zealand’s
most famous metamorphic rock.
1. Name the three different types of rocks. 

2. The word igneous comes from the Latin word ‘ignis’ meaning “fire”. Why do you think
scientists chose to use this word to name these type of rocks? 

3. Explain why the crystals in basalt are small but those in granite are large. 


4. Give four examples of igneous rocks, other than those named in question 3. 

5. Briefly outline how sedimentary rocks are formed. 



6. Give two examples of sedimentary rocks. 
7. Complete the following paragraph by filling in the missing words.
When rocks are buried deep within the Earth, they are subjected
to high and . This causes the sedimentary
rocks to change into rocks.
8. Give two examples of metamorphic rocks and state what rock they are formed from.
(a) comes from  .
(b) comes from  .