Types of rocks

Igneous rocks• Igneous comes from the Latin word ignis meaning

‘fire’

• Igneous rocks are formed when molten material from within the Earth cools and becomes solidMolten material = magma when below the Earth’s surface

lava when above the Earth’s surface

• Igneous rocks are divided into two groups: Intrusive Extrusive

Intrusive igneous rocks

• Intrusive igneous rocks are formed when magma cools slowly below the Earth's surface

• Intrusive means ‘forced in’• Intrusive igneous rocks contain large

interlocking crystals

• Example: Granite

Extrusive igneous rocks

• Extrusive igneous rocks are formed when lava cools down quickly above the Earth’s surface

• Extrusive means ‘pushed out’• Extrusive igneous rocks contain very small

crystals or none at all

• Example: Basalt

Sedimentary Rocks

• Sedimentary comes from the Latin word sedimentum meaning ‘settling’ and sedere meaning ‘to sit down’

• Sedimentary rocks are made from sediment, which is itself made from small, broken-down bits of other rocks and remains

• The material of sediment has been compressed and stuck together, as process known as lithification

Metamorphic rocks• Metamorphic comes from the Greek words meta

meaning ‘change’ and morphe meaning ‘form’• Igneous, sedimentary and metamorphic rocks can

all be changed into ‘metamorphic rocks’ by heat and pressure within the Earth

• Metamorphic rocks are stronger than the original material

• Example: Marble (from Limestone)

The rock cycle

Questions

• Why is marble sometimes used to make chopping/cutting boards?

• If granite is formed underground how is it that granite boulders can been seen above ground?

What type of rock am I?

• Each group had one bag of three ‘types of rocks’ (2 of each per group)

• Without opening the bag, look at the ‘rock models’ and discuss which model represents which type of rock

• Igneous?• Sedimentary?• Metamorphic?