(Chapter 9: Rocks and Minerals); What are rocks made of and Types of rocks

What are rocks made up of?

• Rocks are made of minerals.
• Rock may contain one or more minerals.
• Minerals are the building blocks of rocks; each rock is a mixture of one or more minerals.
• A single Rock may be made up of grains of different colors.
• The screens are of naturally occurring substances known as minerals.

Types of rocks

The type of a rock depends on the quality, the quantity and arrangement of minerals in it.

The earth’s crust is made of three main types of rocks. Each one of them is found in a different way.

Igneous rock

• Igneous rocks are formed by the cooling and hardening of hot liquid Rock material, that lies in huge underground pockets of the earth which Is called magma.
• Magma gets pushed upward towards the surface of the earth because of the pressure inside. On the surface, it cools to form solid rock which is called igneous rock.
• Some of the Magma cools and hardens below the surface of the earth while some flow out of the Earth's surface and then hardens to form igneous rocks.
• The Magma that reaches the surface of the earth is called Lava.
• Igneous rocks are also called fiery rocks.

Types of igneous rocks

Igneous rocks are of different types depending on the kind of minerals Magma contains and the size of the mineral particles.

Different types of igneous rocks are as follows

Granite

• Granite is formed when Magma cools slowly under the surface of the Earth.
• It is very hard and has large grains.
• The color of the granite depends upon the content of its feldspar.
• Granites are white grey pink-red or black depending on the mixture of minerals it contains.

The three main minerals in granite are

• Quartz
• Feldspar
• Mica

Uses

• Granite is very hard in easily used in making buildings and statues
• Polished granite is used for flooring.
• Small pieces of granite are used to make foundations for buildings and for paving roads.

 

Pumice

Pumice is a light color igneous rock that is formed when frothy            Lava cools quickly on the Earth’s surface.

As it cools, the gases in the froth remain trapped inside.      

The reason why Pumice has many holes and pockets which are formed by the gases trapped inside at the time of its formation. Pumice looks like a sponge with holes and pockets in it. Pumice is a light Lava rock that is light grey or cream-colored.

Uses

• Dentists use powder pumice for polishing our teeth.
• Pumice is also used as a body scrubber and also to polish furniture and floors.

Obsidian

• Obsidian is another Lava rock.
• It looks almost like a Black glass.

Uses

• Obsidian because of its sharp edge is used to make cutting tools.

Basalt

• Basalt is a fine-grained and glassy igneous rock.
• Basalt is formed when volcanic Lava cools very fast and hardens quickly above the surface of the earth after coming in contact with air.

Sedimentary rock

• Sedimentary rocks are formed from older rocks that have been broken into tiny fragments.
• Sedimentary rocks are formed from pebbles sand mud or clay that are deposited in rivers lakes seas and oceans.
• At the bottom of these water bodies, all these fragments sink to the bottom and form layers called sediments.
• As the layer of sediments builds up the layer below gets squeezed together. The layers are cemented together by minerals.
• Over millions of years, the pressure turns this layer into Hard rocks such rocks are known as sedimentary rocks.
• Some kinds of sedimentary rocks are formed from the shells of tiny sea creatures. And the others are formed from dissolved minerals that settle by the side of oceans.
• Scientists can find out about life on earth by studying sedimentary rocks because the traces of ancient plant and animal life fossils are found in them.
• These may be shells, bones of animals, prints of leaves, or footprints.

Sandstone

• Sandstone is made from particles of send that get cemented together.
• Sandstone is a common sedimentary rock.
• Sandstone consists mostly of a mineral called quartz.
• Sandstone may be yellow, brown red or pink colored.

• Uses  - Sandstone is commonly used in making buildings for example the Red fort is made out of red sandstone.

Shale

• Shale is made up of clay and mud particles that are piled up in layers.
• It is smooth.

Uses - Shale is used to make tiles and bricks.

Conglomerates

• The conglomerate is a rock of uneven texture.
• It looks like pebbles cemented together with minerals.
• It is formed from pebbles And gravel cemented together by minerals and sand and carried by water.
• Conglomerates are found mostly in shades of grey and orange

​​​​​​​Uses

The conglomerate is used as an ornamental rock and also used for polishing ornaments.

Limestone

• Limestone is made up of mineral calcite which was once a part of animal shells.
• This calcite comes from the shells and skeletons of tiny sea creatures.
• When this animal dies their shells and skeletons settle on the seabed and form layers.
• It is mostly grey or white.

Metamorphic rocks

• Metamorphosis means change. Metamorphic rock is the result of the transformation of existing rock.
• Metamorphic rock their original is sedimentary or igneous rock.
• Tons and tons of pressure that favor heat buildup change them to metamorphic rock.
• Deep inside the earth heat and pressure can bring about changes in their minerals. This changes their appearances and makes them tougher and harder.
• In some metamorphic rocks, the minerals are broken into smaller ones while in others the minerals are stretched into flat particles.

Types of metamorphic rocks

Marble

• Marble is formed when limestone, a sedimentary rock undergoes changes.
• It is found in different colours, white being the most common.
• It can be carved and polished easily. Polished marble gleams.

Uses

• Marble is used to making statues and buildings.
• Taj Mahal is made of white marble.

Slate

• Slate is made by the metamorphosis of shale a sedimentary rock.
• Slater shiny and easily split into thin sheets.
• Slate is found in grey and other colours.

Uses - Slate is used to making slate, blackboards and roofs of buildings.

Gneiss

• Gneiss is a metamorphic rock formed by the metamorphosis of granite.
• It has a light and dark bands.
• It is of course green and has irregular bands of different colours.
• They often glitter because they contain shiny mineral mica.

Quartzite

Quartzite is formed by the metamorphosis of sandstone.

Uses - Quartzite is too hard to be used as a building stone but it is used for making statues.