Plutonic

Part of speech: adjective

Pronunciation: /pluːˈtɒnɪk/

Definitions

1. Relating to igneous rocks formed by solidification of magma deep beneath the Earth's surface
2. Describing geological structures formed through the cooling and solidification of magma that occurs at depth within the Earth's crust
3. Pertaining to rocks created by magma cooling beneath the ground, typically deep within the Earth’s crust

Etymology: Plutonic belongs to a family of geological terms named after Pluto, the Roman god of the underworld, whose name the Greeks gave to the dark realm of the dead. The Earth's interior is the "underworld" of this vocabulary: rocks that cool slowly far below the surface, away from air and weather, are the ones this word describes. The adjective is built from "pluton", a term for a large mass of igneous rock that has solidified underground, combined with the suffix "-ic", which turns a noun into an adjective meaning "relating to" or "characteristic of". The source word itself is a deliberate geological coinage. Its clipped form "pluton" derives from the Greek god's name, so the word pairs a classical myth with a modern scientific label. The term's meaning is narrow but precise. It refers to the origin of the rock, not its composition, so a granite might be called plutonic while a basalt that erupted onto the surface would be called volcanic. That distinction, separating slow underground cooling from rapid surface cooling, is the whole point of the word.

Synonyms: intrusive, magmatic