Rocks and the Rock Cycle | Types, Definition, Characteristics, Formation

What is a Rock?

A rock is a solid composed of a collection of different minerals. Rocks are generally heterogeneous or made up of precise structures that can be described by scientific formulas. Scientists often classify rocks according to how they were made or formed. There are three main types of rocks: metamorphic, igneous, and sedimentary.

Different Types of Rocks:

Metamorphic Rocks – Metamorphic rock that forms under the action of considerable heat and pressure. They are usually found inside the earth’s crust, where there is enough heat and pressure to form rocks. Metamorphic rocks are usually made up of other rocks. For example, shale, a sedimentary rock, can change or metamorphose into a metamorphic rock such as schist or gneiss. Other examples of metamorphic rocks include marble, anthracite, soapstone, and slate.

Igneous Rocks – Igneous rocks are formed by volcanoes. When a volcano erupts, it spews out molten rock called magma or lava. Eventually, the magma will cool and harden, when it reaches the Earth’s surface or somewhere in the crust. This magma or hard lava is called igneous rock. Examples of igneous rocks include basalt and granite.

Sedimentary RocksĀ – Sedimentary rock is formed after many years of compaction and hardening of sediment. Generally, something like a stream or river will carry a lot of small pieces of rock and minerals to a larger body of water. These blocks will sink to the bottom and over a very long period of time (perhaps millions of years) they will turn into solid rock. Some examples of sedimentary rocks are shale, limestone, and sandstone.

The Rock Cycle

Rocks are constantly changing in what is known as the rock cycle. It takes millions of years for rocks to change.

Here is an example of a rock cycle that describes how a rock can change from igneous to sedimentary to metamorphic over time.

Molten rock or magma brought to the surface of the earth by volcanoes. It cools and forms an igneous rock.

Then time, or rivers, and other events will slowly break this rock into small pieces of sediment.

As sediment accumulates and hardens over the years, sedimentary rocks are formed.

Gradually this sedimentary rock will be covered by other rocks and deep in the earth’s crust.

When the pressure and heat are high enough, the sedimentary rock metamorphoses into a metamorphic rock and the cycle begins again.

One thing to note is that stones do not need to go through this particular cycle. They can go from one type to another and vice versa in any order.

Space Rocks

There are actually rocks that come from space called meteorites. They may have different elements or mineral compositions than typical Earth rocks. In general, they consist mainly of iron.

Interesting Facts about Rocks

The word “igneous” comes from the Latin word “ignis” which means “fire“.

An ore is a mineral-bearing rock containing important elements such as metals such as gold and silver.

Sedimentary rocks form layers at the bottom of oceans and lakes.

Marble is a metamorphic rock formed when limestone is exposed to high temperatures and pressures inside the Earth.

The layers of sedimentary rock are called stratigraphy.

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