Crystallization in the rock cycle refers to the formation of rock crystals in cooling magma.

There are three kinds of rock: igneous, sedimentary, and metamorphic.

The rock cycle begins with molten rock (magma below ground, lava above ground), which cools and hardens to form igneous rock. Exposure to weathering and erosional forces, break the original rock into smaller pieces.

This process is called deposition. During deposition particles of rock are laid down in layers. Heavier particles are normally dumped first and then covered by finer material. Layers of sediment build up over time. These layers form a sedimentary sequence.

Crystallization or crystallisation is the process by which a solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. The first is nucleation, the appearance of a crystalline phase from either a supercooled liquid or a supersaturated solvent.

Igneous rocks form when magma (molten rock) cools and crystallizes, either at volcanoes on the surface of the Earth or while the melted rock is still inside the crust. When lava comes out of a volcano and solidifies into extrusive igneous rock, also called volcanic, the rock cools very quickly.

When lava reaches the surface of the Earth through volcanoes or through great fissures the rocks that are formed from the lava cooling and hardening are called extrusive igneous rocks. Some of the more common types of extrusive igneous rocks are lava rocks, cinders, pumice, obsidian, and volcanic ash and dust.

volcanite

Rocks that cool quickly, especially the outer layers of a flow, are primarily composed of glass particles and tiny mafic minerals. This is why the outer surface of a flow is black. The most abundant felsic mineral in lava rock is plagioclase feldspar, which gives the surfaces a waxy luster.