Metamorphic Rock

Definition

Metamorphic rock is a type of rock that has been transformed from an original rock type, known as the parent rock, through the process of metamorphism. This transformation occurs due to changes in temperature, pressure, and chemical processes, which alter the mineral composition and structure of the rock. Metamorphic rocks play a crucial role in understanding geologic processes and are integral to the rock cycle, showcasing how rocks can evolve from one form to another over time.

5 Must Know Facts For Your Next Test

1. Metamorphic rocks can be classified into two main types: foliated and non-foliated, based on their texture and mineral alignment.
2. Common examples of metamorphic rocks include schist, gneiss, and marble, which originate from shale, granite, and limestone respectively.
3. The formation of metamorphic rocks often occurs deep within the Earth’s crust, where high temperatures and pressures are prevalent.
4. Metamorphism can result from both contact with hot magma (contact metamorphism) and from regional tectonic forces (regional metamorphism).
5. Metamorphic rocks are essential indicators of tectonic activity and provide insights into past geological environments and conditions.

Review Questions

• How do the processes of heat and pressure contribute to the formation of metamorphic rocks from parent rocks?
  • Heat and pressure are fundamental in the formation of metamorphic rocks as they cause physical and chemical changes in the parent rock. When a rock is subjected to high temperatures, minerals can become unstable and recrystallize into new minerals that are stable at those conditions. Similarly, increased pressure can lead to the realignment of minerals within the rock, resulting in foliation or other textural changes. Together, these processes transform the original rock into a new metamorphic rock with distinct properties.
• Compare and contrast foliated and non-foliated metamorphic rocks, providing examples of each.
  • Foliated metamorphic rocks exhibit a layered or banded appearance due to the parallel alignment of mineral grains under directional pressure. Examples include schist and gneiss. In contrast, non-foliated metamorphic rocks lack this layered structure and have a more uniform texture because they are formed under equal pressure conditions or contain minerals that do not show foliation. Marble is a prime example of a non-foliated metamorphic rock, formed from limestone.
• Evaluate the importance of metamorphic rocks in understanding Earth's geological history and tectonic processes.
  • Metamorphic rocks are crucial for piecing together Earth's geological history as they serve as indicators of past environmental conditions and tectonic activity. By studying their formation conditions and mineral compositions, geologists can infer historical temperature gradients and pressures present during mountain-building events or continental collisions. This knowledge helps construct models of Earth's dynamic processes over time, revealing insights into the nature of plate tectonics and the evolution of the planet's crust.

Related terms

Parent Rock: The original rock from which a metamorphic rock is formed, also known as the protolith.

Metamorphism:

The process by which rocks are changed in mineralogy, texture, and chemical composition due to extreme conditions of heat and pressure.

Foliation:

The alignment of mineral grains within a metamorphic rock that results from differential pressure, giving the rock a layered appearance.