Explanation: The agent of the contact metamorphism is the heat, pressure and the differential stress and the chemically active fluids. Where the heat is sufficient to cause the process of the metamorphism and the contracts with the igneous body and thus the rocks that are produced by this process are never foliated.

Pressure

During metamorphism the mineral content and texture of the protolith are changed due to changes in the physical and chemical environment of the rock. Metamorphism can be caused by burial, tectonic stress, heating by magma, or alteration by fluids.

Contact metamorphism occurs typically around intrusive igneous rocks as a result of the temperature increase caused by the intrusion of magma into cooler country rock. The area surrounding the intrusion where the contact metamorphism effects are present is called the metamorphic aureole or contact aureole.

Contact metamorphism occurs anywhere that the intrusion of plutons occurs. In the context of plate tectonics theory, plutons intrude into the crust at convergent plate boundaries, in rifts, and during the mountain building that takes place where continents collide.

Metamorphism therefore occurs at temperatures and pressures higher than 200oC and 300 MPa. Rocks can be subjected to these higher temperatures and pressures as they become buried deeper in the Earth. Such burial usually takes place as a result of tectonic processes such as continental collisions or subduction.

The shock metamorphism shows evidence for two major impact processes on evolved and primordial lunar surfaces: (1) shocked silica phases with minor Al contents formed from plagioclase-rich primordial crusts of the Moon, and (2) shocked quartz formed by silica-rich target rocks, especially on evolved parts of the Moon.

The main factors that control metamorphic processes are: The mineral composition of the parent rock. The temperature at which metamorphism takes place. The amount and type (direction) of pressure during metamorphism. The amount and type of fluid (mostly water) that is present during metamorphism.

Metamorphism is the change of minerals or geologic texture (distinct arrangement of minerals) in pre-existing rocks (protoliths), without the protolith melting into liquid magma (a solid-state change). Metamorphism produced with increasing pressure and temperature conditions is known as prograde metamorphism.

In a physical change, matter may change its size, shape, or state, but its chemical properties do not change. Because the chemical properties of matter remain the same in a physical change, a physical change is often easy to reverse.

What is happening when rocks are broken down by both physical and chemical changes? Acids can dissolve the minerals in rock.

They are also physical changes because they do not change the nature of the substance. Boiling waterBoiling water is an example of a physical change and not a chemical change because the water vapor still has the same molecular structure as liquid water (H2O).

Water boiling, melting ice, tearing paper, freezing water and crushing a can are all examples of physical changes. On the other hand, chemical changes are a bit different. In a chemical change, a new substance is formed. The chemical change also usually involves heat, burning, or other interaction with energy.

In a physical change the appearance or form of the matter changes but the kind of matter in the substance does not. However in a chemical change, the kind of matter changes and at least one new substance with new properties is formed. The distinction between physical and chemical change is not clear cut.

Chemical Changes are also called Chemical Reactions. The chemical reaction produces a new substance with new and different physical and chemical properties. Matter is never destroyed or created in chemical reactions. The particles of one substance are rearranged to form a new substance.