Metamorphic rocks Flashcards
How do metamorphic rocks form?
Metamorphic means that the rock has changed form. Metamorphic rocks form when high temperature pressure alter existing igneous rocks and sedimentary rocks. Rocks change into metamorphic rocks when it experiences intense heat and extreme pressure. These changes can be physical and chemical.
What are types of metamorphism?
Metamorphic rocks can be formed deep beneath the earths surface when the pressure is really high. A great weight of the rock above means pressure can be thousands of times greater than the pressure of the atmosphere at the earths surface. It can also get much hotter the deeper it is into earths crust and mantle. The temperatures can be hundreds to thousands of degrees and this heat alone can alter rocks. This also means the lower part of the earths crust is mostly metamorphic rocks. Extreme heat and pressure can also be caused by movement of tectonic plates. Metamorphism over a wide area is described as regional metamorphism. Another type is when rocks come in contact with magma as it is rising to the surface. This is called contact metamorphism.
What are two metamorphic changes in a rock?
Heat and pressure can melt rock, causing a process called recrystallisation where new crystals grow as the rock cools down. When the rock is molten new particles can move around and new minerals can form in this process. This is why metamorphic rocks contain many more different minerals than igneous rocks.
Another metamorphic change is in the teture of the rock. Minerals in these rocks can become squashed or flat or into long needle shapes. The rock may then develop layers or bands in a process called foliation. The amount of bands depends on the amount of heat and pressure.
