Which is the metamorphic rock among the following? (A) Granite (B) Quartzite (C) Granodiorite (D) Rhyolite

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Points to Remember:

  • Metamorphic rocks are formed from existing rocks (protoliths) that have been changed by heat, pressure, or chemical reactions.
  • Igneous rocks are formed from the cooling and solidification of magma or lava.
  • Sedimentary rocks are formed from the accumulation and cementation of sediments.

Introduction:

The question asks to identify the metamorphic rock from a given list of rock types. To answer this correctly, we need to understand the processes that form different rock types. The rock cycle illustrates how igneous, sedimentary, and metamorphic rocks are interconnected through geological processes. Igneous rocks, like granite and rhyolite, form from the cooling of molten rock. Sedimentary rocks form from the accumulation and lithification of sediments. Metamorphic rocks, on the other hand, originate from the transformation of pre-existing rocks (igneous, sedimentary, or even other metamorphic rocks) under conditions of high temperature, pressure, or both, often involving chemical reactions.

Body:

Understanding Rock Types:

  • Igneous Rocks: These rocks are formed from the cooling and solidification of magma (molten rock beneath the Earth’s surface) or lava (molten rock on the Earth’s surface). Granite and granodiorite are examples of intrusive igneous rocks (formed from magma cooling slowly beneath the surface), while rhyolite is an extrusive igneous rock (formed from lava cooling quickly at the surface).

  • Sedimentary Rocks: These rocks are formed from the accumulation and cementation of sediments (fragments of other rocks, minerals, or organic matter). Examples include sandstone, shale, and limestone.

  • Metamorphic Rocks: These rocks are formed from the transformation of pre-existing rocks due to changes in temperature, pressure, or chemical environment. The original rock (protolith) is altered without melting. This process can change the rock’s mineral composition, texture, and structure.

Analyzing the Options:

(A) Granite: An intrusive igneous rock, formed from the slow cooling of magma.

(B) Quartzite: A metamorphic rock. It is formed from the metamorphism of sandstone, where the quartz grains are recrystallized under high temperature and pressure.

(C) Granodiorite: An intrusive igneous rock, similar to granite but with a different mineral composition.

(D) Rhyolite: An extrusive igneous rock, formed from the rapid cooling of lava.

Conclusion:

From the analysis above, it is clear that Quartzite (B) is the only metamorphic rock among the given options. Granite, granodiorite, and rhyolite are all igneous rocks formed through different cooling processes of magma or lava. Therefore, understanding the formation processes of different rock types is crucial for correct identification. Further geological studies, including microscopic analysis and chemical testing, can confirm the classification of rocks. A comprehensive understanding of the rock cycle and the processes that shape our planet is essential for sustainable resource management and geological hazard mitigation.

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