Extrusive igneous rock.
Igneous rocks do form on the earths surface. A volcano erupts and the lava that comes out cools and hardens forming igneous rocks.
a volcano erupts
Over time the magma chamber found inside volcanos is cut off from the mantle by tectonic plate movement. Without constant exchange of hot magma from the mantel to replace the colder magma in the volcano, (convection), the magma inside the volcano hardens into igneous rock.
An island
Everytime a volcano erupts, the magma gets higher and higher everytime it hardens. This causes an island arc
Any kind of volcano can form after the eruption. If it doesn't erupt and never has then it isn't a volcano.
Melted rock that forms inside the Earth is called magma. When magma rises to the surface and erupts through a volcano, it is referred to as lava. Magma can solidify underground to form igneous rocks once it cools and crystallizes.
When lava reaches the surface, it quickly hardens into rock. The resulting rock will have either a glassy texture (with no crystals) or have a fine-grained texture (with small crystals) because the minerals have little or no time to crystallize.
The rock forms over a cooling process.
It will form extrusive igneous rock. Beyond that they exact type will vary.
igneus rock
Extrusive igneous rocks