Plutonic

Plutonic refers to igneous rocks that crystallize below the surface from cooling magma. The term comes from Pluto, the god of the underworld, reflecting deep subterranean formation. Plutonic rocks contrast with volcanic (extrusive) rocks, which erupt at the surface and cool rapidly.

They typically have a coarse-grained, phaneritic texture in which crystals are large enough to see with the naked eye. This texture results from prolonged cooling within the crust, often at depths of several kilometers to tens of kilometers.

Plutonic rocks include granitic, granodioritic, dioritic, tonalitic, and mafic varieties, spanning felsic to mafic compositions. The rocks commonly form large intrusive bodies called plutons, and can be exposed at the surface after uplift and erosion as batholiths, stocks, or laccoliths.

Formation occurs when magma intrudes existing rock and solidifies before reaching the surface. Crystallization preserves mineral assemblages that help infer crustal processes, temperature, and pressure history. Some plutons are associated with metamorphism and ore deposits; their crystallization ages are often determined by radiometric dating.

Plutonic rocks are distinguished from their volcanic counterparts by mineralogy and texture, with a general presence of visible crystals and the absence of glassy textures. In geological literature, the word also extends to the body of rock formed by such crystallization, termed a pluton.

If "Plutonic" appears in other contexts, it may be used as a name or title; however, the geological sense is by far the most common usage.