Types of Rocks: Igneous, Sedimentary, and Metamorphic Rocks Explained with Examples

Different Types of Rocks you might observe in your surroundings. Have you ever picked up a shiny pebble or kicked a rough stone on the road and wondered, “How was this rock actually made?”Just imagine, deep inside the Earth, extremely hot molten material cools down slowly to form one type of rock. Far away on the surface, tiny sand particles settle layer by layer to make another layer. 

This article focuses completely on the rocks, their different types, with many examples found in nature. 

Table of Contents

• What is Rock?
• Different Types of Rocks and Examples

What is Rock?

Rocks are all around us, on mountains, riverbanks, roads, and even in your garden. But each rock has a long story to tell about its journey inside the Earth.

In simple language, 

“Rocks are naturally occurring solid materials made of minerals.”

They can be hard or soft and are composed of one or more minerals or mineral-like matter. Their colour, texture, hardness, and even the way they break can change based on how they are formed.

Different Types of Rocks and Examples

Rocks found in nature rarely show simple characteristics, and they usually exhibit some variation in different sets of properties as per the measurement scale changes.
In nature, all rocks are grouped into three main types:

• Igneous Rocks

• Sedimentary Rocks

• Metamorphic Rocks

Now, let's discuss types of rocks and examples in detail in the next section.

Igneous Rocks

Igneous rocks are formed when magma or lava cools and solidifies.

• Magma → molten rock inside the Earth
• Lava → molten rock that comes out during a volcanic eruption

As the hot liquid cools, it turns solid and forms igneous rock.

You may wonder after knowing that igneous rocks can form with or without crystals, either deep inside the Earth as intrusive (plutonic) rocks or on the surface during volcanic eruptions as extrusive rocks. 

Magma is formed when existing rocks in the Earth’s mantle or crust partially melt. This melting happens due to three main factors: 

• an increase in temperature
• a drop in pressure 
• a change in the rock’s composition.

Here is an interesting fact to remember, 

About 90% of the Earth’s crust is made up of igneous rocks!

Now, let's discuss the types of Igneous Rocks. There are two types of igneous rocks:

• Intrusive Igneous Rocks form deep beneath the Earth’s surface. Since they cool very slowly, they develop large, visible crystals.

 Example: Granite, Diorite, Pegmatite

• Extrusive Igneous Rocks form on the surface of Earth during volcanic eruptions. They cool very quickly, so their crystals remain small, and some even appear smooth or glassy.

Example: Basalt, Pumice, Tuff.

Sedimentary Rocks

Sedimentary rocks are formed when tiny pieces of rocks, minerals, or dead plants and animals settle down, get compressed, and turn into solid rock. This settling process is called sedimentation.

You will often find sedimentary rocks near rivers, lakes, seas, and deserts.

You will be amazed after knowing that, Sedimentary rocks sometimes have fossils, remains of plants or animals from millions of years ago!

Now, let's discuss the types of Sedimentary Rocks in detail

• Clastic Sedimentary Rocks are formed from broken fragments of pre-existing rocks that get compacted and cemented over time.

 Examples: Sandstone, Siltstone

• Chemical Sedimentary Rocks form when dissolved minerals in water settle out and solidify as the water evaporates.

Examples: Limestone, Iron ore

• Organic Sedimentary Rocks are created from the accumulated remains of plants and animals that get compressed into solid rock.

 

 Examples: Coal, some types of Dolomite

Now, next time, when you visit a nearby riverbank and observe the sand layers. Notice how some layers are thick, while others are thin; that is, sedimentation in action!

Metamorphic Rocks

Metamorphic rocks start off as igneous or sedimentary rocks. But deep inside Earth, due to high heat and pressure, they change form.
This process is called metamorphism (meaning “change in form”).

 

The best example is limestone, which becomes marble after deep-earth transformations.

There are two main Types of metamorphic rocks. Let's discuss them. 

• Foliated Metamorphic Rocks form when rocks are exposed to strong heat and pressure, causing minerals to align in layers or bands.

 

Examples: Gneiss, Phyllite

• Non-foliated metamorphic Rocks form under heat and pressure but without any layering, giving them a smooth, uniform appearance.

 

Examples: Marble, Quartzite

Types of Rocks in India

India’s landscape is full of different rock systems:

• The Archaean System includes some of the oldest rocks on Earth, mainly gneiss, found in Karnataka, Andhra Pradesh, Tamil Nadu, and nearby regions.
• The Dharwar System consists of very old sedimentary rocks that are mostly found in Karnataka.
• Cuddapah System contains sandstone, limestone, and marble, commonly seen in Rajasthan.
• The Vindhyan System is known for red sandstone and is mainly found in Madhya Pradesh.
• The Gondwana System is rich in coal-bearing rocks and is mostly spread across Madhya Pradesh.
• Deccan Trap features basalt rocks formed from ancient volcanic eruptions, covering large areas of Maharashtra and Gujarat.
• The Tertiary System includes younger rock formations found mainly in the Himalayan region.
• The Quaternary System consists of the youngest deposits, widely found across the Indus and Ganga plains.

So far, you have learned how rocks are formed and how each type tells a unique story about Earth’s processes. From fiery igneous rocks to layered sedimentary ones and transformed metamorphic rocks, our planet continually shapes and reshapes the materials beneath our feet.