8.4-Metamorphic Rocks

Formation of Metamorphic Rocks
1. Metamorphic rocks form when intense heat and/or pressure alter existing rocks.
2. When intense heat and/or pressure alter existing rocks, it may cause physical changes
3. The process called shearing is the folding of rocks or sliding different parts of rock sideways in a process called shearing.
4. Heat and pressure can also cause chemical changes, such as recrystallisation minerals. New minerals such as the semiprecious gemstone garnet may form during this process.
5. As rocks get buried deeper, the temperature & pressure increase. Heat & Pressure can also increase the movement of the Earths Crust. The crust is broken into massive plates, called tectonic plates.
6. The formation of rocks is called metamorphism.
Types Of Metamorphism
1. Regional Metamorphism- this is where rock is altered by both heat & pressure. This kind of metamorphic change often occurs across large areas as a result of colliding plates or rocks being buried.
2. Contact Metamorphism- this is where rock is altered mostly by heat, It often occurs over smaller areas as a result of hot magma intruding into rock.
3. Dynamic Metamorphism- this is where the rock is altered mostly by heat. It often occurs over a small area where the crustal rocks are scraping past each other.
Metamorphic Changes
1. The texture of a rock can be changed by metamorphism. One common change for a rock placed under heat & pressure is that it becomes foliated.
2. Foliation is the movement of minerals into layers or bands.Pressure can also squash & crumple layers or bands, making them wavy.
3. Not all metamorphic rocks are foliated. Examples of non-foliated metamorphic rocks are marble & quartzite.
4. At the temperature of over 1000, the carbon can crystallise into diamond. Diamonds can be transported to the surface millions of years later by fast moving magma

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8.4-Metamorphic Rocks

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