Igneous Rocks

Formation of Igneous Rocks - Fill in the Blanks

Igneous rocks are formed from the cooling and solidification of molten magma which originates in the earth's mantle.There are two types of Igneous Rocks.

Basalt is an extrusive igneous rock. It forms when magma pours out on to the Earth's surface as lava during a volcaniceruption. The lava cools very quickly giving little time for large crystals to form. Basalt is a very hard rock, black in colour and contains microscopic crystals, if any. The hexagonal columns making up the Giant's causeway in County Antrim is a spectacular example of basalt formed from volcanic activity in Northern Ireland over 60 million years ago.

Intrusive Granite is an intrusive igneous rock as the magma does not reach the surface of the Earth. The magma cools Slowly inside the crust of the Earth. As a result, Large crystals form a characteristic feature of this rock. Granite occurs in the Mourne Mountains of County Down and also formed over 60 million years ago during the Tertiary Era.

Example | Type | Characteristics

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granite | igneous | - pale in colour

-impermeable

-very hard

-micro crystals

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basalt. | igneous. | - both pale and dark in colour

-large crystals

2) a. state one thing that granite and basalt both have in common.

b. state three ways in which basalt and granite are different.

c. why are the crystals found in granite very large?

a)both igneous rocks

b) -

• pale/dark in colour

• different sized crystals

• one dries slower

c) it takes longer to dry which gives them more time to form