How Are Metamorphic Rocks Formed? Processes and Real-World Examples
They are a class of rocks that result from the alteration of pre-existing rocks in response to changing environmental conditions or any natural situations without any liquefaction process, such as fluctuations with temperature, pressure, and mechanical stress, and the inclusion or subtraction of any available chemical components.
Definition and Examples
Metamorphic rocks arise from the transformation of existing natural rock substances to new types of rock without any exterior liquefaction manually done, in a process called metamorphism. During this process, the original rock is subjected to temperatures of more than 150-200 degrees celsius and often pressures of more than 100 megapascals resulting in vast physical and chemical modifications.
Types and Characteristics
Common metamorphic rocks varieties include phyllite, schist, gneiss, quartzite, and marble.
Metamorphic rocks can be classified into two main categories based on the way they are formed - those that are foliated as they have been formed due to high pressure and under shear stress and those that are not foliated under any form of pressure.
Types of Metamorphism
The three major types of metamorphism are Contact, Regional, and Dynamic metamorphism.
Contact Metamorphism occurs when hot lava comes in contact with an already existing body of rock. When this happens the existing rock's current temperature rises and also becomes infiltrated with fluid from the volcano.
Regional Metamorphism occurs over a much larger surface area. This type of metamorphism produces and forms rocks such as gneiss and schist. Regional metamorphism is mainly caused by large geologic processes such as mountain-building.
Dynamic Metamorphism, like regional metamorphism, also occurs because of mountain-building. These huge forces of heat and pressure that are applied naturally cause the rocks to be bent, folded, crushed, flattened, and sheared in any manner. As hard as or even harder than igneous rocks, metamorphic is almost always harder than sedimentary rocks. They form the roots of many mountain chains and are exposed to the surface after the softer outer layers of rocks are eroded away due to any natural calamities caused.
FAQs on Metamorphic Rocks: Definition, Types, and Key Characteristics
1. What are metamorphic rocks, as per the CBSE syllabus?
Metamorphic rocks are one of the three main types of rocks. They are formed when existing parent rocks, which can be igneous, sedimentary, or even other metamorphic rocks, are changed by intense heat and pressure deep within the Earth's crust. This transformation process, known as metamorphism, alters the rock's original mineral composition and texture without melting it. The name itself comes from Greek words meaning "to change form."
2. How are metamorphic rocks formed?
Metamorphic rocks are formed through a process called metamorphism, driven by two primary factors:
- Heat: This can come from magma rising through the crust or from the rock being buried deep within the Earth, where temperatures are much higher.
- Pressure: This is caused by the immense weight of overlying rock layers or from the compressional forces of tectonic plates colliding.
3. What are the two main types of metamorphic rocks? Provide some examples.
Based on their texture, metamorphic rocks are classified into two main groups:
- Foliated Rocks: These have a layered or banded appearance caused by the parallel alignment of minerals under pressure. Examples include slate (formed from shale), schist, and gneiss.
- Non-Foliated Rocks: These rocks do not have a layered look because their minerals are not aligned. They typically have a more uniform, crystalline texture. Examples include marble (formed from limestone) and quartzite (formed from sandstone).
4. How do metamorphic rocks differ from igneous and sedimentary rocks?
The key difference lies in their formation process. Igneous rocks are formed from the cooling and solidification of molten rock (magma or lava). Sedimentary rocks are formed from the compaction and cementation of sediments like sand and mud. In contrast, metamorphic rocks are formed when any existing rock is fundamentally changed by heat and pressure, altering its original structure into a new form.
5. What are some real-world uses of common metamorphic rocks like marble and slate?
Metamorphic rocks are highly valued for their durability and appearance. For instance:
- Marble is extensively used for making sculptures, monuments like the Taj Mahal, and for decorative purposes in buildings, such as flooring, tabletops, and countertops.
- Slate has the unique property of splitting into thin, durable sheets, which makes it an excellent material for roofing tiles, blackboards, and floor tiles.
- Quartzite is extremely hard and resistant, making it a valuable material for construction and building stone.
6. What are 'index minerals' and why are they important for studying metamorphic rocks?
Index minerals are specific minerals that form only under a particular range of temperature and pressure. When geologists find minerals like garnet, kyanite, or sillimanite in a metamorphic rock, it acts as a geological 'thermometer' and 'pressure gauge'. Their presence helps scientists determine the specific conditions—also known as the grade of metamorphism—that the parent rock was subjected to deep within the Earth.
7. Can a metamorphic rock undergo metamorphism again?
Yes, a metamorphic rock can be transformed again if the conditions of heat and pressure change. This is a key concept in the rock cycle. For example, a metamorphic rock like schist, if subjected to even higher temperatures and pressures, can re-metamorphose into a higher-grade rock like gneiss. This shows that the process of rock transformation is continuous and dynamic.
