In this paper, we give a detailed discussion of metamorphic rocks. There is a brief discussion about the origin of metamorphic rocks and some of the circumstances that result in the formation of the rocks. Having introduced the reader to the origin of the rocks, the paper gives a further discussion on how these kinds of rocks are formed and the necessary conditions if the process of metamorphism has to take place. In the end, the paper describes the two major categories of these rocks and giving some of the distinguishing features of the two categories.
Metamorphic rocks are those kinds of rocks that have been formed from underlying sedimentary rocks. Metamorphic rocks originate from a number of extensive changes that take place in the texture and the parent rock’s mineralogy. This is a process that takes place due to changes of temperature and pressure occurring above the digenesis point and below the rock that is to melt. In order for metamorphism to take place, the rock should remain solid so that eventually a metamorphic rock can be formed. Should the parent sedimentary rock melt during the process, an igneous rock will be formed (Pough & Peterson, 1997). Basically, metamorphic rocks will originate from the process of metamorphism taking place on the sedimentary rocks due to increased temperatures and pressure without melting.
Formation of Metamorphic Rocks
Having understood the origin of these rocks, it is very easy to explain their formation. The formation of these rocks results from extensive temperatures and pressure (Cefrey, 2003). In order for metamorphism to take place, energy is very important since it acts as the fuel for the necessary chemical reactions on the sedimentary rocks hence resulting in the metamorphic rocks. Metamorphic rocks will therefore be defined as rocks that have resulted from the morphed process from one kind of rock to another. The source rocks are the sedimentary and igneous rocks which have to be under intensive pressure from the overlying earth materials.
Categories of Metamorphic Rocks
Different schools of thought have tried to give varied categories of metamorphic rocks, but there are two major categories of metamorphic rocks that have been accepted by the majority of geologists around the world. These are foliated and non-foliated metamorphic rocks. Foliated metamorphic rocks are the ones that have resulted from slate and phyllite (Pough & Peterson, 1997), and will have branded appearances. They can as well be identified from their chemical compositions. These rocks will often tend to be fine-grained with very many mineral compositions. On the other hand, the non-foliated rocks are constituted of one mineral, and the reason they are termed to be monomineralic. A good example of this is marble which is formed once limestone has undergone the metamorphic process (Cefrey, 2003).
References
Cefrey, H. (2003). Metamorphic rocks: London: Allyn and Bacon.
Pough, F. & Peterson, R. (1997). A field guide to rocks and minerals. Oxford: Oxford University Press.