Characteristics of Metamorphic Rock

The term metamorphism means “change of form” that arise from the transforming of a rock type. These rocks constitute an integral part in the earth crust forming about 12% of Earth’s surface. Classification of these rocks can be made based on texture, mineral facies and chemicals. The formation of these rocks occur due to excessive temperature and pressure from the layer of rocks above, these rocks can also form due to shift in tectonic plates occurring due to continental collisions that generates horizontal pressure, distortion and friction. Metamorphic rocks are formed from heat collisions due to the intrusion of magma from the interior parts of Earth. Extensive study about metamorphic rocks provides with various kinds of information ranging from temperature, pressure happening deep within the Earth’s crust. Rocks like marble, gneiss, schist, gneiss are examples of metamorphic rocks.

The process of metamorphism is based on the change in structure of existing rocks through application of extreme pressure and heat or by using chemical properties of fluid. This change in chemical composition makes structural changes for the minerals that make the rocks. Modification in structure includes restructuring of minerals to form layers of aggregated minerals in parts within the rock. The rock, which undergoes metamorphism remains a solid rock throughout the process. The rock does not melt most of the time, but at the highest form of metamorphism is when the rocks start to melt partially, during the process when the conditions of metamorphism surpasses, the rocks enter the igneous part in the rock life cycle.

Metamorphic rocks help to understand the processes occurring down the earth surface due to the changing physical and chemical conditions inside the crust of the earth. This provides the geologists varieties of information regarding creation of mountain ranges, collision between continents, movement of oceanic plates and the phasing of sea-water through the oceanic crust. The different kinds of rocks like sedimentary rocks, igneous rocks and metamorphic rocks can transform into a metamorphic rock on application of pressure and heat to change the chemical and physical nature of the rock melting entirely. Extreme application of pressure leads to foliation by which the flat layers forming inside the rocks are squeezed with pressure. Foliation occurs due to application of external pressure in one direction, but metamorphic rocks can also be non-foliated.

There are two distinctive type of metamorphism, which are both related to heat inside the Earth surface:

Regional Metamorphism: Due to extreme pressure, change in large chunks of rocks spread over a wide area, due to extreme pressure from compression due to geological forces or pressure from overlying rocks. Rocks are exposed to high temperature due to deep burial.

Contact Metamorphism: Occurrence of change in rock structure after contact with magma, due to extreme heat is termed as contact metamorphism.

There are ample reasons due to which, a rock undergoes metamorphism, the minerals of a rock are in a stable condition if there is a limited range of temperature, pressure and chemical conditions. The change is subjected due to chemical changes, replacement of minerals by new minerals and stable minerals in new condition.

Effects of Temperature and Pressure on Rocks

There are various ways pressure and heat can cause rocks to change like dehydration of minerals, which constitute the rock. Rearranging of atoms within the mineral structure, change of the rock into another mineral, which is of the same composition but having different physical properties. The rocks are made of different minerals and change in composition of a single mineral changes the properties of the rock. With the change in mineral composition due to effect of heat on the rock surface, the composition of minerals changes. This occurs due to the change in atomic structure of various minerals present in a rock that causes the rock type to change from one to another.

Deformation of rocks can occur due to strain energy, which is released from the rock mass after excavation in a place. The part of the strain energy released is dissipated due to fracturing of rocks that causes the deformation to occur. Poor rock conditions lead to collapsing of rocks, which can bring about a lot of natural disasters on a large scale. The rock in certain situations is not displaced beyond a certain angle from a viewpoint of operation. The rock minerals in high stress exceeds elastic limit, where the relation is established using Hooke’s law.

Metamorphic rocks transform shape and structure on various occurrence due to heat as well as pressure where the chemical composition of rock changes on account of various implementations of heat and pressure causing strain on the rocks physical as well as chemical composition.