This is obsidian. It is an Igneous rock which means it is made by the cooling of lava. Igneous rocks cool super fast that they don't have time to make crystals.
You are probably wondering what is the difference between lava and magma? The difference is lava is above ground and magma is below ground. In the picture the red hot stuff shooting out of it is lava and the red hot stuff in the volcano is magma.