The Earth's Crust: Three Types of Rocks
Classified in Geology
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The Earth's crust is made up of three main types of rocks: igneous, sedimentary, and metamorphic.
Igneous Rocks
Igneous rocks are formed when magma (molten rock) cools and solidifies. They can be classified into two main types: intrusive and extrusive.
- Intrusive igneous rocks are formed when magma cools and solidifies slowly beneath the Earth's surface.
- Extrusive igneous rocks are formed when magma cools and solidifies quickly on the Earth's surface.
Sedimentary Rocks
Sedimentary rocks are formed when sediments (pieces of other rocks, minerals, or organic matter) are compacted and cemented together.
- Clastic sedimentary rocks are formed from the accumulation of broken pieces of other rocks.
- Chemical sedimentary rocks are formed from the precipitation of minerals from water.
- Organic sedimentary rocks are formed from the accumulation of plant or animal remains.
Metamorphic Rocks
Metamorphic rocks are formed when existing rocks are changed by heat, pressure, or chemical reactions.
- Contact metamorphism occurs when rocks are heated by contact with magma.
- Regional metamorphism occurs when rocks are subjected to high temperatures and pressures over a large area.
- Hydrothermal metamorphism occurs when rocks are altered by hot water.