Physical Geography 102
Igneous Rocks


Igneous Rocks

Rocks that formed from the cooling and crystallization of magma
Igni- (Latin) =
-ous (Latin) =

Origin of Magma

Magma - liquid rock or molten rock
Needed to make magma:
1)
2)

Volatiles

Products given off by material as a vapor or gas
Water and carbon dioxide
Volatiles will lower the melting temperature

Heat

Increased temperature will cause melting
Sources of heat in the Earth's interior:
Radioactivity
1)
2)
3)
4)
5)

Partial Melting

Different materials melt a different temperatures.
Partial melting is the melting of some of the material in a rock but not the entire rock.
The composition of a magma will be different from the composition of the rock if the rock is not completely melted.

Crystallization

Reversal of melting resulting from:
Cause by:

Sequence of Crystallization

Partial melting says that different material melt at different temperatures
Different materials solidify or crystallize at different temperatures

Igneous Rocks

Additional information on classification and identification of igneous rocks can be found at:
Atlas of Igneous Rocks
Igneous Rocks Identification Exercise