Minerals and Rocks
Concept: Minerals and Types of Rocks
What are Minerals?
Minerals are inorganic substances formed naturally in the earth and constitute earth’s rocks, sand and soil.
Example: Talc, quartz, feldspar.
Properties of Minerals:
- Physical characteristics of minerals are determined based on their colour, hardness, lustre and texture.
- Mohs Scale determines the hardness of a mineral.
- The softest mineral is talc, whereas the hardest is diamond.
- The study of minerals is called Mineralogy.
Types of minerals:
| Metallic minerals | Non-metallic minerals |
|---|---|
|
The minerals from which metals can be extracted economically. Example : Haematite, Bauxite, Pyrite. 
Haematite |
The minerals which do not contain any metal component. Example : Diamond, Clay, Mica. 
Diamond |
Ores:
The metallic minerals that we use in our day-to-day lives do not exist in free forms in nature; rather, they remain in combined forms. Ores are those rocks from which metallic minerals can be mined for economic purposes. In other words, ores are mineral-rich rocks.
Example: Bauxite is an ore of the metal aluminium.
Some important metallic minerals and their ores:
| S. no. | Name of ore | Mineral extracted |
|---|---|---|
| a. | Borax | Sodium |
| b. | Bauxite | Aluminium |
| c. | Carnalite | Potassium |
| d. | Epsom | Magnesium |
| e. | Calcite, Gypsum | Calcium |
| f. | Cuprite, Pyrite | Copper |
| g. | Calamine | Zinc |
| h. | Haematite, Magnetite | Iron |
What is a Rock?
A rock is a naturally occurring solid mass comprising one or more minerals.
Example: Sandstone, shale, basalt, gneiss.
Types of Rocks:
Rocks are classified based on the quality, quantity and arrangement of the minerals.
Igneous Rocks:
- These rocks are also called fiery rocks because they are formed from hot molten lava.
- Molten magma that comes out of the volcanoes and spreads over the earth’s surface is called lava.
- As soon as the molten lava comes out, it starts to cool down and gradually solidifies over time to form igneous rocks.
Sedimentary rocks:
- These rocks are formed by the fragmentation of older rocks by natural forces.
- As the name suggests, sedimentary rocks are formed by the deposition of sediments of sand, mud or clay.
- The layers of sediments are deposited and cemented together by minerals that harden over time to form sedimentary rocks.
- Sedimentary rocks are of scientific importance because scientists use them to analyse the fossils of plants and animals that are embedded in the sedimentary rocks.
Metamorphic Rocks:
- The term metamorphic stands for change.
- Metamorphic rocks are formed due to changes in the existing sedimentary and igneous rocks.
- These changes occur as a result of high temperature and pressure.
New Words:
Inorganic substances: Substances that do not originate from plants and animals.
Lustre: The way how light reflects on the surface of a mineral. It is an important property of minerals.
Fossils: Remains of prehistoric plants and animals that remain embedded in rocks and preserved over millions of years.
Temperature: The degreen of hotness or coldness of a body.
Did You Know?
- There are around 4000 minerals found on the earth's surface.
- Sulphides are one of the oldest ores. They were formed due to the increased amount of sulphur released due to volcanic activity.
- Aluminium is the most common element found in the earth’s crust.
- The world-famous Pyramids of Giza were built using limestone.
- Igneous rocks can be of two types—intrusive igneous rocks and extrusive igneous rocks.
- Almost 95% of the earth’s crust is made of igneous rocks.
