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Igneous rocks are formed from the cooling and solidification of molten rock, either magma within the Earth's crust or lava on the surface. They are one of the three main types of rocks, alongside sedimentary and metamorphic rocks. Igneous rocks are characterized by their crystalline texture and can be either intrusive (formed deep underground) or extrusive (formed on the surface).

Key characteristics and formation:

Magma/Lava:

The starting material for igneous rocks is magma, molten rock beneath the Earth's surface, or lava, magma that has erupted onto the surface.

Cooling and Solidification:

As magma or lava cools, it crystallizes and solidifies, forming igneous rocks.

Intrusive vs. Extrusive:

Intrusive (Plutonic): Formed when magma cools slowly beneath the Earth's surface, resulting in coarse-grained rocks like granite.

Extrusive (Volcanic): Formed when lava cools rapidly on the Earth's surface, resulting in fine-grained or glassy rocks like basalt or obsidian.

Chemical Composition:

Igneous rocks can be classified based on their chemical composition, which determines their mineral content and appearance. For example, rocks can be felsic (rich in silica), mafic (rich in iron and magnesium), or intermediate.

Examples:

Common examples of igneous rocks include granite, basalt, rhyolite, obsidian, and pumice.