Extrusive:
Extrusive is the outside of the earth and it refers to the mode of igneous volcanic rock formation. The Hot magma from inside the earth flows out onto the surface as it explodes violently into the atmosphere. This is intrusive rock formation, in which magma does not reach the surface. Also, the main effect of extrusion is that the magma can cool much more quickly in the open air or under sea water and there is little time for the growth of crystals. Instead becoming the natural glass or obsidian
the magma contains it which are released as free gas then it may cool with large or small bubble shapes.