Describe the characteristics and types of primary rocks.
Primary rocks, also called igneous rocks, form the base of the Earth’s crust. They are created when molten rock material cools and solidifies—magma beneath the surface or lava on the surface. These rocks are usually hard, non-porous, and free of fossils because the intense heat during their formation destroys organic matter. One of their main features is a crystalline structure, as minerals lock together while cooling. The size of these crystals depends on how quickly the rock cools: slow cooling creates large, visible crystals, while rapid cooling leads to very fine grains or even a glassy texture.
There are two main types of igneous rocks. Intrusive (plutonic) rocks form deep underground, where magma cools slowly, producing large crystals—granite is a common example. Extrusive (volcanic) rocks form when lava cools quickly on the surface, resulting in fine-grained textures, like basalt, which makes up much of the ocean floor.
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Important Questions from GS1
How far is it correct to say that the First World War was fought essentially for the preservation of the balance of power?
How far was the Industrial Revolution in England responsible for the decline of handicrafts and cottage industries in India?
The groundwater potential of the Gangetic valley is on a serious decline. How may it affect the food security of India?
What are aurora australis and aurora borealis? How are these triggered?
What is a twister? Why are the majority of twisters observed in areas around the Gulf of Mexico?
