Types of Igneous Rocks
"There
are
two main types
of igneous rocks:
extrusive and intrusive."
Intrusive Igneous Rock
The intrusive ones are the rocks that are formed when magma cools inside the Earth's mantle.
These rocks are generally coarse grained because the cooling has been slow and the minerals have had a fairly long time to grow.
Such rocks are for example granite, syenite, monzonite, diorite, gabbro, kimberlite, dunite and peridotite.
They can often be seen as large boulders, which have been formed in a large pluton, then lifted, and exposed by erosion of weaker, surrounding rock.
Granite in Yosemite National Park. By jimmyharris
Extrusive Igneous Rock
The extrusive ones are the rocks that form when magma erupts out of a volcano on the Earth's surface.
These rocks are generally fine grained because the cooling is quick for them and the minerals don't get much time to grow.
Some can have holes left behind by air or gas bubbles.
Such rocks are rhyolite, andesite, dacite, trachyte, latite, scoria, basalt and obsidian.
They can sometimes be seen as lava tubes, and quite often as columns which were formed when lava cooled.
But they can also just cover the ground.
Basalt colums, Teneriffa. By 126 Club
Pyroclastic Rocks
Porphyritic Rock
Pegmatite
Back to Igneous Rocks
