Rocks and Minerals - 1 Class 5 Notes Science

All land on the earth is made up of soil and rocks. Long ago the ground was mostly solid rock.
The grains that make up rocks are composed of naturally occurring substances called minerals.

Rocks of Different Colours

• All rocks on the earth are made up of minerals. 
• Some rocks contain only one mineral. Others can contain up to six or more minerals. 
• Rocks are of different colours based on the different minerals present in them. 
• Rocks and minerals are called natural resources since they provide us with many metals, non-metals, and fossil fuels.

Rocks

A rock is a solid natural object composed of minerals. Rocks are made up of minerals. Some rocks contain only one mineral while others contain many minerals. Metals are found in the rocks in the form of minerals.

• Rocks are like mixtures of minerals, and each rock has its own special blend of properties like what minerals it has, how big the grains are, and how it feels. 
• We use different systems to group rocks based on their characteristics. In nature, rocks aren't always simple and can have variations in their properties depending on how closely we look at them.

Types of Rocks

Rocks on the earth are formed in three different ways. Based on their formation types, they are divided into three groups—igneous rocks, sedimentary rocks, and metamorphic rocks.

1. Igneous Rocks

• Igneous rocks are formed by the cooling and hardening of hot molten rocks. The hot molten rock flows out through a volcano.
• Hot molten rock, when present inside the Earth, is called magma and when it flows on the Earth’s surface, it is called lava.
• Magma or lava cools down and hardens to form igneous rocks. About 95% of the Earth’s crust is made up of igneous rocks. Igneous rocks contain many minerals like mica and feldspar.

Formation of Igneous Rocks 

Types of Igneous Rocks

(i) Granite: It is a very hard rock. It is formed by the slow cooling of magma below the Earth’s surface. It is rich in quartz, feldspar, and mica. It comes in many colours. It is used for making kitchen counters, floors, etc.

(ii) Pumice: It is a light-colour igneous rock. It has many holes which are formed by the gases trapped in the lava at the time of its formation. It is lightweight and can float on water. It is used in polishing the floors. Dentists use powdered pumice for polishing our teeth.

Types of Igneous Rocks

(iii) Obsidian: It is a shiny and smooth igneous rock formed by the quick cooling of lava. It is used for making jewellery. It is also used to make cutting tools.
(iv) Basalt: It is formed by the cooling of lava on the earth’s surface. It is dense and dark. It is used for constructing roads.

2. Sedimentary Rocks

• Water, wind, rain, and snow break away big rocks. The rock particles so formed are carried away by wind and flowing water into rivers, lakes, and seas.
• These rock particles settle at the bottom of the water bodies and form layers.
• The layers are cemented together by minerals. Repeated deposition of layers presses down the lower layers and then turns them into rocks. Such rocks are called sedimentary rocks.
• Sedimentary rocks are also formed from the shells of sea creatures.
• About 75% of the rocks found on the surface of the Earth are sedimentary rocks.
  
  Formation of Sedimentary Rocks

Types of Sedimentary Rocks

(i) Sandstone: It is a soft stone made from particles of sand that get cemented together. The most common mineral found in sandstone is quartz. This rock is used in construction. The Red Fort in Delhi and Agra Fort in Agra are made of red sandstone.
(ii) Conglomerate: It is made from pebbles, gravel, and boulder cemented together by minerals and sand. It has a very uneven texture and is used in construction.
(iii) Shale: It is made from clay particles cemented together. It is used to make bricks and tiles.
(iv) Limestone: It contains the mineral calcium and shells of sea creatures. It is used to make cement, lime, glass, and bricks. Chalk is a form of limestone.
Types of Sedimentary Rocks

3. Metamorphic Rocks

Metamorphic rocks are formed due to changes in the existing rocks over time. They can be formed from sedimentary or igneous rocks due to high temperature and pressure.
Metamorphic Rocks

Types of Metamorphic Rocks

(i) Marble: It is formed from limestone, a sedimentary rock. It is used for making statues, floors, and slabs.
(ii) Slate: It is formed from shale, a sedimentary rock. Both shale and slate can split into thin layers. It is used for making blackboards and handheld writing boards (slates).

(iii) Gneiss: It is formed from granite. It has light and dark bands. It is used in construction.
(iv) Quartzite: It is formed from sandstone. It is a very hard rock and it is used for making glass and jewellery.

Minerals

All rocks are made up of minerals. Minerals are chemical substances that occur naturally on the Earth. Minerals can be metallic or non-metallic.
Minerals

Types of Minerals

(i) Metallic Minerals

• Metallic minerals contain metals such as gold, iron, aluminium, and copper.
• Such minerals are called ores. Metallic minerals are usually associated with igneous rocks. They are hard and have a shine of their own.
• Gold and silver are commonly used for making jewellery.
• Iron, copper, and aluminium are used for making cooking utensils. Copper is used to make electric wires. Mercury is used for making thermometers.

(ii) Non-metallic Minerals

• Non-metallic minerals are generally associated with sedimentary rocks.
• They are usually not hard and have no shine of their own.
• Graphite, mica, asbestos, potassium, magnesium and feldspar are non-metallic minerals.  
• Precious stones such as diamonds or rubies are also non-metallic.

Fossil Fuels

Fossil fuels are fuels formed by natural processes such as the decomposition of dead and buried organisms.

Coal: 

• Coal is a kind of sedimentary rock. Millions of years ago, the Earth was covered with thick swampy forests.
  
  Coal
• When plants died, they fell into the swamps and got buried.
• Due to high temperatures and pressure, these plants get converted into coal.
  
  Formation of coal
• Coal is used as fuel for cooking, for producing electricity, and in steam engines.

Petroleum: 

• It is also called crude oil, rock oil, or black gold.
  
  How petroleum is taken out from under the ground
• It is formed from the remains of dead plants and sea animals which got buried under the sea millions of years ago.
• It is mostly used as a fuel in different forms like petrol, diesel, kerosene, and Liquefied Petroleum Gas (LPG). It is also used for dry cleaning.
• Coal and petroleum are not technically considered to be minerals as they are formed from organic matter.
• Besides being used as fuel, coal, and petroleum are used for making important chemicals such as medicines, cosmetics, fertilizers, plastics and many others.

Need for Conservation of Coal and Petroleum

• Coal and petroleum were formed millions of years ago from dead and decaying animals and plants buried in the soil.
• They are very limited resources and once they are finished they cannot be replaced.
• Hence, it is very necessary to conserve these resources by using them carefully.
• Alternative forms of energy like solar energy, water energy, and wind energy should be used.

Uses of Rocks and Minerals

• Rocks and minerals have various important uses in our daily lives. They serve as the basic materials for constructing things like our homes, schools, roads, and bridges.
• Some rocks provide us with essential fuels, such as coal, petroleum, and uranium. Uranium, a type of mineral, is especially valuable for generating nuclear energy.
• Certain rocks contain metals that are handy for making items we use every day. For example, aluminum and iron from rocks are used to create utensils, while copper is utilized in making electric wires.
• In addition, rocks contribute to the world of jewellery by providing us with gemstones. Well-known gemstones like diamond, ruby, emerald, and sapphire are all minerals extracted from rocks.