1. Igneous Rocks
* Formation: Formed from the cooling and solidification of magma (molten rock) or lava.
* Process:
* Intrusive igneous rocks: Magma cools and solidifies underground. This slow cooling allows large crystals to form, resulting in rocks like granite.
* Extrusive igneous rocks: Lava erupts onto the Earth's surface and cools quickly. This rapid cooling leads to smaller crystals or even a glassy texture, like basalt.
2. Sedimentary Rocks
* Formation: Formed from the accumulation, compaction, and cementation of sediments, which are fragments of pre-existing rocks, minerals, or organic matter.
* Process:
* Weathering and Erosion: Rocks are broken down into smaller pieces by wind, water, ice, or chemical reactions.
* Transportation: Sediments are carried by wind, water, or ice to new locations.
* Deposition: Sediments settle in a basin or depression.
* Compaction: The weight of overlying sediments compresses the deposited material.
* Cementation: Dissolved minerals precipitate between the sediment grains, acting as a glue to bind them together.
3. Metamorphic Rocks
* Formation: Formed when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are transformed by heat, pressure, or chemical reactions without melting completely.
* Process:
* Heat: The intense heat from deep within the Earth or from nearby magma bodies alters the minerals in the rock.
* Pressure: The weight of overlying rocks or tectonic forces can cause the minerals to recrystallize, creating new textures.
* Chemical Reactions: Hot fluids circulating through the rock can react with minerals and cause changes in their composition.
Key Differences:
* Igneous rocks: Formed from molten rock.
* Sedimentary rocks: Formed from fragments of other rocks.
* Metamorphic rocks: Formed from existing rocks that are transformed by heat, pressure, or chemical reactions.
The Rock Cycle:
These three rock types are interconnected through the rock cycle. Rocks can be transformed from one type to another over millions of years through processes like weathering, erosion, heat, pressure, and melting.
