extrusive

1. Tending to push or thrust out.
2. Tending to protrude or project.
3. Derived from magma poured out or ejected at the earth's surface. Used of igneous rocks.

Refers to ingeous rocks erupted on the surface.

Describing lava that reached the earth's surface or igneous rock formed from such lava, characterized by a glassy or fine crystalline texture.

The adjective has one meaning:

Meaning #1: (geology) of rock material; forced out while molten through cracks in the earth's surface
  Antonym: intrusive (meaning #2)