Paragraph on “Rocks and Their Types” complete paragraph for Class 9, Class 10, Class 11 and Class 12

Rocks and Their Types

Fusion of dust particles, under pressure, in outer space formed the first rocks. These rocks then formed most of the planets. Most of the  Earth’s surface is made up of rocks this includes the Mountains, stones, pebbles and the soil which is also made of finer particles of rock. We have rocks which are about 3,900 million years old. Based on their mode of formation, rocks can be classified into three types.

The first type called ‘Igneous Rocks’ are formed because of the cooling of molten volcanic lava. Under the surface of the Earth, rocks are in molten state and on occasions they are thrown up on the surface by volcanoes. The molten material then cools down to form rocks of this type. Cooling of lava below the Earth’s surface also results in the forming of Igneous rocks. Granite is a good example of this type. The 680bn d type of  rocks are called ‘Sedimentary rocks’. Rivers are constantly carrying away with them layers of top soil and pieces of rock, these are deposited in river basins and deltas. Over a period of time the deposits get compressed due to pressure and Sedimentary rocks are formed. Shale and Limestone are examples of this type.

‘Metamorphic rocks’ are the third type of rocks. These are formed due to the Earth’s internal heat and pressure acting upon Sedimentary and Igneous rocks. This action hardens the rocks and forms new ones, as an example Shale turns into Slate and soft Limestone, turns into hard Marble. Metamorphic transformations take place under the surface of the Earth and these rocks are generally revealed after the upper layers are eroded. Rocks are made up of minerals, which are important or precious to man. Minerals which include larger quantities of metals are called ‘Ores’ like Gold and Iron, and those which don’t have metals are called ‘Precious stones’ like Diamonds, Rubies and Sapphires.