Question

How do igneous rocks form?

Answer 1

Hint: Rocks are naturally-occurring solid masses on the earth’s surface that are made up of various minerals. They make up to a large part of the earth’s crust and a smaller part of the upper mantle. Based on the process of their formation, rocks can be divided into three main categories—igneous, sedimentary and metamorphic. Igneous rocks form around 15% of the Earth's current land surface while sedimentary rocks cover 73% of the same and around 12% of the earth’s surface is made up of metamorphic rocks.

Complete answer: Igneous rocks are made up of volcanic material like magma, volcanic ash and such. During a volcanic eruption, the magma contained in the earth’s mantle gushes out as lava on the earth’s surface which solidifies to form extrusive igneous rocks. Another process includes the magma seeping into cracks of pre-existing rocks in the earth’s crust and crystallises to form intrusive igneous rocks. There are different types of intrusions based on shape and size and some of them are batholiths, stocks, laccoliths, sills, dikes, etc. Examples of extrusive rocks are basalt, pumice, scoria, etc and intrusive rocks are granite, gabbros, diorite, etc.

Note: Sedimentary rocks are formed due to accumulation of minerals and organic matter in layers on top of each other over time. Examples of sedimentary rocks include sandstone, conglomerate, dolomite, flint, iron ore limestone, shale, coal, etc. Metamorphic rocks, on the other hand, are formed due to changes in the minerals and geological texture of pre-existing rocks due to heat and pressure. Examples of metamorphic rocks include anthracite, gneiss, hornfels, marble, phyllite, schist, slate, etc.