AskDefine | Define extrusive

Dictionary Definition

extrusive adj : of rock material; forced out while molten through cracks in the earth's surface [ant: intrusive]

User Contributed Dictionary



  1. jutting out; extruding

Extensive Definition

Extrusive refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff. This is opposed to intrusive rock formation, in which magma does not reach the surface.
The main effect of extrusion is that the magma can cool much more quickly in the open air or under seawater, and there is little time for the growth of crystals. Often, a residual portion of the matrix fails to crystallize at all, instead becoming an interstitial natural glass or obsidian.
If the magma contains abundant volatile components which are released as free gas, then it may cool with large or small vesicles (bubble-shaped cavities) such as in pumice, scoria, or vesicular basalt.
extrusive in Indonesian: Ekstrusi (geologi)
extrusive in Italian: Roccia ignea effusiva
extrusive in Polish: Ekstruzja
extrusive in Simple English: Extrusive
extrusive in Finnish: Ekstrusiivikivi
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