plutonik

Plutonik is a term used in geology to describe intrusive igneous rocks that crystallize below the Earth's surface. The standard English spelling for these rocks is plutonic, while plutonik (or similar variants) appears in some languages or older writings as an alternative transliteration. The concept refers to magma that cools slowly underground, forming coarse-grained textures and large mineral crystals.

Intrusive rocks formed in this manner are commonly grouped as plutonic rocks and include granite, diorite, granodiorite, tonalite, and related lithologies. They contrast with volcanic (extrusive) rocks, which crystallize at or near the surface and typically exhibit a fine-grained or glassy texture due to rapid cooling. Plutonic rocks are often organized into plutons, which are intrusive bodies that can range from small stocks to large batholiths.

Key features of plutonic rocks include a phaneritic texture, where crystals are large enough to be seen with the naked eye. Mineralogy varies from felsic to intermediate compositions, dominated by feldspar and quartz, with biotite, hornblende, or other ferromagnesian minerals less common in more felsic variants. Plutonic rocks form in a variety of tectonic settings, notably at continental collision zones and above subduction zones, and they contribute to the growth and stabilization of continental crust.

Etymology traces to Pluto, the god of the underworld, reflecting the deep, subterranean formation of these rocks. The term emphasizes the contrast with surface rocks formed by surface eruptions and rapid cooling.