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Protoliths refer to the original rocks from which metamorphic rocks are formed. Metamorphic rocks are formed as a result of weather, temperature and chemical effects on an igneous rock. Protoliths form the basic differences between a metamorphic rock and the other classes of rocks i.e sedimentary and igneous rocks, these other classes of rocks do not form from protoliths, therefore, the study and understanding of protoliths is tremendously crucial in the description of a metamorphic rocks.

Protoliths are the igneous rocks forms which are the building blocks of metamorphic rocks. Before a protolith can form a metamorphic rock, it must undergo a series of environmental changes. This diverse change in conditions is what accounts for the many metamorphic rocks available on earth today. Protoliths when naturally buried deep in the earth crust encounters high temperature due to the high amount of magma in the crust. These high temperatures combined with the fluid chemical contents acting on the protolith results in the formation of metamorphic rocks. The level of temperature during the process of formation causes the occurrence of different types of metamorphic rocks. Some protoliths experience only partial contact with the heat of their formative environment. The relationship between a protolith and its emerging metamorphic rock is mutual because most of the components of the protolith remains in the metaphoric rocks formed.

Protolith of a metamorphic rock can be identified in two ways, these include textural identification and identification by chemical composition. The textural identification involves identifying the protolith in recognizing the physical layout of the mother rock. This, however, is only possible in low grade metamorphic rocks due to the fact that they have only undergone exposure to low temperature and thus still retain some of their physical properties. The identification by chemical composition is done by studying the chemical compositions within the metamorphic rock and comparing it with those of other igneous rocks to determine which one was its protolith.

Protoliths find their applications in differentiating metamorphic rocks, also offering the means of naming metamorphic rocks since most metamorphic rocks are named after their protoliths. Some basic examples of protoliths and the metamorphic rocks they form are, serpentine which forms the, rock serpentinite, quartz arenites, which forms the quartzite, peroditites or dunites, which forms the rock soapstone, shale which forms mudstones.

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