Tending to extrude or push outward; in geology, relating to igneous rock that has erupted onto Earth's surface (opposite of intrusive).
From extrude plus -ive, meaning 'tending to do something.' In geology, this term was coined in the 19th century by scientists studying volcanic rock formation.
Here's where this word gets really cool: geologists use 'extrusive' to describe lava that erupts onto the surface (like basalt from volcanoes), while 'intrusive' describes magma that cools underground—same hot rock, but 'extrusive' rocks literally pushed themselves outward onto Earth's surface!
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