The are many different types of volcanic rock, from granite to crystals. They range is size and colour and are formed under different conditions. Igneous rock is the name for volcanic based rock which is put under high heat and pressure. They all start from magma and are formed during the cooling process as they get further away from the heat.
There are two classifications for the rock – intrusive and extrusive.
This rock can be found inside the volcano and it’s cone. Granite has been formed here. Because it is still very hot inside the volcano, this rock cools very slowly, allowing large crystals to form during this process. Intrusive rocks have a course grain because of this long cooling process.
Flung from the volcano as tephra or lava, the molten rock cools very quickly on contact with the outside air. This leaves very little time for crystals to form and so they are fine-grained. They can also have gas bubbles in them, making them very light and porous.
Different types of rock are created in different volcanoes, depending on their location and volcano type.