Metamorphic rocks start off as igneous, sedimentary, or other metamorphic rocks. These rocks are changed when heat or pressure alters the existing rock’s physical or chemical make up.

Metamorphic rocks started out as some other type of rock, but have been substantially changed from their original igneous, sedimentary, or earlier metamorphic form. Metamorphic rocks form when rocks are subjected to high heat, high pressure, hot mineral-rich fluids or, more commonly, some combination of these factors.

Metamorphic rocks

Metamorphic rocks form from heat and pressure changing the original or parent rock into a completely new rock. The parent rock can be either sedimentary, igneous, or even another metamorphic rock. The word “metamorphic” comes from Greek and means “To Change Form”.

rock cycle

There are three kinds of rock: igneous, sedimentary, and metamorphic. Igneous rocks form when molten rock (magma or lava) cools and solidifies. Sedimentary rocks originate when particles settle out of water or air, or by precipitation of minerals from water.

As the lava cools it hardens and becomes igneous rock. As soon as new igneous rock is formed, the processes of weathering and erosion begin, starting the whole cycle over again!…When the particles are carried somewhere else, it is called erosion.

• Transportation.
• Deposition.
• Compaction & Cementation.

The Rock Cycle

• Weathering. Simply put, weathering is a process of breaking down rocks into smaller and smaller particles without any transporting agents at play.
• Erosion and Transport.
• Deposition of Sediment.
• Burial and Compaction.
• Crystallization of Magma.
• Melting.
• Uplift.
• Deformation and Metamorphism.

The formation of clastic and organic rocks begins with the weathering, or breaking down, of the exposed rock into small fragments. Through the process of erosion, these fragments are removed from their source and transported by wind, water, ice, or biological activity to a new location.

A useful way to illustrate how the three main types of rock are related to one another and how changes to rocks happen in a recurring sequence is the rock cycle. It can be presented in a diagram like the one below.

approximately 20 million years

Many of Earth’s key processes function in cycles and rock cycle is no exception. The rock cycle is a web of processes that outlines how each of the three major rock types—igneous, metamorphic, and sedimentary—form and break down based on the different applications of heat and pressure over time.

Explanation: Some igneous rocks are eroded and turned directly to sedimentary rocks. Some sedimentary layers have ended up on the continental plates. This is a complete rocks cycle, but not all rocks go though this process.

The cycle has no beginning and no end. Rocks deep within the Earth are right now becoming other types of rocks. Rocks at the surface are lying in place before they are next exposed to a process that will change them.

The rock cycle continues. Mountains made of metamorphic rocks can be broken up and washed away by streams. New sediments from these mountains can make new sedimentary rock. The rock cycle never stops.

Weathering. All rocks may seem permanent and unchanging over a human lifetime, but this apparent permanence is an illusion created by our short observational time frame. Over geologic time, water and air attack rocks of all kinds at Earth’s surface through the process called weathering.

Weathering and erosion, transport and deposition would all effectively stop. Scientists believe that, if all these active processes of the rock cycle ceased to operate, then our planet would cease to be able to support any life.

Erosion is an important step in the formation of sedimentary rocks, let alone the entire rock cycle. If there is no erosion, there would be no sediments that would be deposited in different places. In this case, it would affect the shape of the Earth’s surface and some minerals would not be formed.

Humans interact with the rock cycle by mining rocks for useful minerals such as gold and for fuel such as coal, oil and gas. Metals are found within igneous and sedimentary rocks. The metals are deposited when hot metal rich fluids produced by volcanic activity pass through joints in rocks and cool.

What Are the Most Important Types of Rock in the Crust?

• Granite is great stuff! Not only is it my personal favorite, it is without a doubt the most common rock type on the continental land masses.
• Basalt is extrusive.
• As it turns out, most of the ocean floor is basalt, and most of the continents are granite.

Compilations of many rock analyses show that rhyolite and granite are felsic, with an average silica content of about 72 percent; syenite, diorite, and monzonite are intermediate, with an average silica content of 59 percent; gabbro and basalt are mafic, with an average silica content of 48 percent; and peridotite is …

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