The Universe
Our planet
The rock cycle
The rock cycle is Earth’s amazing recycling system where rock constantly change from one type to another over millions of years. This process is driven by heat, pressure, weathering and erosion. It is something like a journey that begins with hot magma that cools into igneous rocks either plutonic or volcanic rocks. They break into fragments called sediments that gets transformed in sedimentary rocks. Heat and pressure can transform them into metamorphic rocks, which can melt back into magma to start again the cycle.
Igneous rocks are formed from the cooling and solidification of molten rock originated from Earth’s mantle of crust. Intrusive or plutonic rocks form from magma cooling and solidifying slowly beneath the Earth’s surface; for example granite. Volcanic or extrusive rocks form from lava or ash cooling rapidly on Earth’s surface after a volcanic eruption, like basalt.
Sedimentary rocks are formed from accumulated fragments of older rocks or chemical precipitates. Rocks break down into small pieces by erosion and weathering; sediments are carried away (transport) and settle in layers in lakes and oceans (deposition). Layers are buried, and sediments change into solid rock (lithification).
There are some types of sedimentary rocks. Clastic or detrital rock are made from pieces of other rocks (conglomerate). Chemical rocks form from minerals precipitating out of water (rock salt, some limestone). Organic rocks form from the remains of living things (coal, chalk).
Metamorphic rocks are formed from existing igneous, sedimentary or even other metamorphic rocks that are transformed by intense heat and pressure, changing their mineral composition without melting. The process is known as metamorphism. Foliate rocks develop layers, for example slate and gneiss; non foliated rocks show crystalline structure, like marble or quartzite.
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