Geography Rocks!!

Welcome back, we hope our map lessons could help you, and today we'll be learning about another important part of geography, which is...you guessed it..ROCKS!!

We need to study rocks, because rocks store a lot of information. They contain clues about what the earth was like in the past, and we can trace the events of the earth, way before humans came into existence with the help of rocks. 

Rocks can answer a variety of questions like: 

•  Was there a lake or volcano where the rock was present?
• Was there a sea?
• Were there mountain ranges?
• Was the atmosphere thick or thin?

And many more such questions, which are really important, for knowing how humans have affected the environment, and to understand the world and its existence. 

Now that we know, that studying rocks are really important, lets speak about the basics in rock study, which would be in your syllabus in Class 9 and Class 10.  

Firstly, rocks are often confused with minerals, however they are different, and this the difference between the two:

Rocks:

A rock is composed of combinations of minerals, each mineral having its own chemical formula and crystalline structure. 

Minerals:

A mineral is a naturally-occurring inorganic (there are some exceptions to this) crystalline solid (though mercury is regarded as a mineral) with a specific chemical composition and a characteristic internal regular geometric arrangement of atoms, sometimes expressed as natural crystal faces. 

Thus, rocks are complex, as they consist of different minerals and have unique shapes, sizes and concentrations. 

Types of Rocks:

Igneous Rocks:

Igneous Rocks are also known as fire rocks, and they are formed either underground or above ground. 

Underground, they are formed when melted rock, called magma deep within the earth become trapped in small pockets. As these pockets cool underground, the magma becomes igneous rocks. 

Also, when volcanoes erupt, lava is spurted out, this lava on cooling, forms the igneous rocks above ground. 

Here are some amazing pictures of igneous rocks : 

                Granite

              Basalt

Sedimentary Rocks:

For thousands, even millions of years, little pieces of our earth have been eroded--broken down and worn away by wind and water. These little bits of our earth are washed downstream where they settle to the bottom of the rivers, lakes, and oceans. Layer after layer of eroded earth is deposited on top of each. These layers are pressed down more and more through time, until the bottom layers slowly turn into rock.

The study of sedimentary rocks and rock strata provides information about the subsurface that is useful for civil engineering. Sedimentary rocks are important sources of natural resources like coal, fossil fuels, drinking water or ores. 

Here are some amazing pictures of sedimentary rocks:

 

                     Coal                                                Conglomerate 

Metamorphic Rocks:

Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". The original rock is subjected to heat and pressure, (temperatures greater than 150 to 200 °C and pressures of 1500 bars) causing profound physical and/or chemical change. The original rock may be sedimentary rock, igneous rock or another older metamorphic rock.

The study of metamorphic rocks (now exposed at the Earth's surface following erosion and uplift) provides information about the temperatures and pressures that occur at great depths within the Earth's crust. Some examples of metamorphic rocks are gneiss, slate, marble, schist, and quartz.

Here are some amazing pictures of metamorphic rocks:

Slate

Marble

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