igneous rocks form when hot, liquid rock, or magma, cools and solidifies.. magma forms in three...
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Igneous Rocks
Igneous rocks form when hot , liquid rock, or magma, cools and solidifies.
. Magma forms in three ways:
1. When a rock is heated.
2. When pressure is released
3. When rock changes composition.
Composition and texture of igneous rocks
Igneous rocks differ from one another in what they are made of and how fast they cooled.
The light-colored rocks are less dense than the dark colored rocks. They are rich in aluminum, potassium, silicon and sodium.
These rocks are called felsic.The dark colored rocks are mafic.They are rich in iron, calcium and
magnesium.
The longer it takes for the magma to cool, the more time the mineral crystals have to grow and the larger the crystals are and coarser the texture is.
The less time magma takes to cool, the less time crystals have to grow.
The rock formed is fine-grained containing small crystals.
Igneous rock formations
Igneous rock formations can be found above and below the surface of the Earth.
Igneous rocks can be:
IntrusiveExtrusive
Intrusive igneous rocks
Intrusive igneous rocks are formed when magma pushes into the surrounding rock below the Earth’s surface and cools.
Common intrusive igneous rock formations are:
1. Batholiths 2. Sills 3. Dike 4.Stocks
Extrusive igneous rocks
Igneous rock that forms from magma that erupts, or extrudes, onto the Earth’s surface is called extrusive igneous rock.
These are common around volcanoes.
When erupts from a volcano, a lava flow forms.
Sometimes lava erupts and flows from long cracks in the Earth’s crust called fissures.
Extrusive igneous rocks
Sometimes large amount of lava flows out of fissures onto land. The lava can cover a large area and form a plain called lava plateau.
The Rock Cycle