What does extrusive mean?
"Extrusive" is chiefly a geological term describing igneous rock that forms when magma erupts onto the Earth's surface as lava and then cools and solidifies in the open air. Basalt, rhyolite, obsidian, and pumice are classic examples: because they cool quickly at the surface, extrusive rocks are typically fine-grained or glassy, often containing gas bubbles frozen into place. This contrasts with "intrusive" rock such as granite, which crystallizes slowly underground and develops large visible crystals. The word derives from the Latin trudere, meaning "to thrust," so it literally conveys material being forced out. Beyond geology, "extrusive" occasionally appears in general English to mean simply jutting or projecting outward, though in everyday speech terms like "protruding" are more common. Its natural opposite is "intrusive," making the pair a tidy illustration of how Latin prefixes encode direction.
(Geology) Of igneous rock: formed from magma that erupted onto the Earth's surface as lava and cooled there.
"Obsidian is an extrusive rock that forms when felsic lava cools too rapidly for crystals to grow."
Almost always found in geological and volcanological writing.
Jutting or projecting outward from a surrounding surface.
"An extrusive knob of granite broke the smooth line of the ridge."
Rare in general usage; "protruding" or "jutting" is more idiomatic.
Every chunk of pumice or basalt you've ever picked up is "extrusive" — literally lava that made it out before it froze.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of extrusive
Extrusive comes from the Latin trudere, "to thrust or push," combined with the prefix ex- ("out") and the adjective-forming suffix -ive. It entered English in the 19th century alongside the development of modern geology, when scientists needed precise vocabulary to distinguish surface-cooled lavas from rocks crystallizing below ground. It shares this root with intrude, protrude, and obtrude — all words about thrusting in different directions — and with its own derivatives extrude and extrusion.
Related word forms
How extrusive is actually used
Primarily a technical term of geology and volcanology; outside scientific contexts the general sense of "projecting" is rare, with words like "protruding" preferred. The adjective is neutral in tone.
Easily confused with extrusive
"Intrusive" describes things that force their way in — including igneous rock that cools beneath the surface — while "extrusive" describes things that are pushed or forced out onto the surface.