3.2 Notes
How are igneous rocks formed?
Objective: Identify two ways that igneous rocks are formed
Molten rock is formed by melted minerals. When molten rock cools, it becomes solid, forming
igneous rock. The temperature of the upper mantle is hot enough to melt minerals to form
molten rock.
Igneous means “formed by fire.” Why are rocks formed from magma
called igneous?
Molten rock inside Earth is called
magma. Magma is found inside Earth’s
upper mantle and lower crust. Magma
rises through cracks in Earth’s crust
then cools and crystallizes. Magma
hardens to form igneous rocks on
Earth’s surface.
Crust 10C
at 300m
Mantle
1,000C at
60km
Outer core
2,200C at
3,000km
Inner core
5,000C at
4,000km
Is this a fast process?
Magma cools inside Earth’s crust to form large bodies of igneous rock. A general name for all
of these bodies of igneous rock is pluton. The types of pluton are: batholiths, stocks, laccoliths,
dikes and sills.
What is magma?
Magma that reaches Earth’s surface is called lava. Lava cools upon contact with air or water.
Igneous rocks form quickly from lava.
How does lava rise to Earth’s surface?