Metamorphic Rocks Introduction

Summary

Metamorphic rocks are one of the three main rock types, along with sedimentary and igneous rocks. They form when existing rocks undergo extreme heat and pressure, transforming them into new structures. The original rock, called the protolith, can be changed into another metamorphic rock. Two types of metamorphism—contact and regional—occur under varying conditions of heat and pressure. Foliation, or the formation of layers, is a key feature of some metamorphic rocks. Examples include gneiss from granite, slate from shale, schist from slate, and marble from limestone.

Takeaways

• 🪨 Metamorphic rocks are one of the three main types of rocks, alongside sedimentary and igneous rocks.
• 🔥 Metamorphic rocks are formed through extreme heat and pressure, changing the structure and form of existing rocks.
• 🔄 The term 'metamorphic' relates to 'metamorphosis,' meaning to change form or structure.
• 🧱 The original rock before metamorphosis is called the 'protolith.'
• 🌍 Metamorphic rocks can form deep within the Earth's crust or through plate tectonic movements and magma intrusions.
• 🌋 Contact metamorphism occurs near igneous intrusions and involves high temperatures but lower pressure compared to regional metamorphism.
• 🏔️ Regional metamorphism occurs over large areas, often at the base of mountains where tectonic plates collide.
• 🔳 Foliation is a key feature of metamorphic rocks, presenting as visible layers or bands formed under pressure.
• 🪶 Examples of metamorphic rocks include gneiss (from granite), slate (from shale), schist (from slate), and marble (from limestone).
• 🧗 Metamorphic rocks can either be foliated or non-foliated, depending on how their minerals have been arranged during metamorphism.

Q & A

What are the three main types of rocks?

The three main types of rocks are metamorphic, sedimentary, and igneous.

How are metamorphic rocks formed?

Metamorphic rocks are formed when existing rocks experience extreme heat and pressure, which changes their physical and chemical makeup.

What is the meaning of the word 'metamorphic' in the context of rocks?

The word 'metamorphic' refers to a change in the form, structure, or characteristics of an object, similar to how metamorphic rocks are transformed from other types of rocks.

What is a 'protolith' in relation to metamorphic rocks?

A protolith is the original rock that undergoes heat and pressure to become a metamorphic rock.

Where can metamorphic rocks form?

Metamorphic rocks can form deep in the Earth's crust, through plate tectonic movements such as collisions, or through magma intrusions into existing rocks.

What are the two main types of metamorphism?

The two main types of metamorphism are contact metamorphism and regional metamorphism.

How does contact metamorphism differ from regional metamorphism?

Contact metamorphism occurs in localized areas, typically near magma intrusions, and involves high temperatures but slightly lower pressure. Regional metamorphism occurs over large areas, typically in regions of tectonic plate collisions, and involves both high temperature and high pressure.

What is foliation in metamorphic rocks?

Foliation is a characteristic of some metamorphic rocks, where they exhibit layering or banding caused by the squishing or elongation of the original rock along a particular axis.

What is an example of a foliated metamorphic rock?

An example of a foliated metamorphic rock is gneiss, which forms from the metamorphosis of igneous rocks like granite.

What are some examples of metamorphic rocks and their protoliths?

Some examples of metamorphic rocks and their protoliths are: gneiss from granite, slate from shale, schist from slate, and marble from limestone.