Compléter Kind of rocks. BasicVersion en ligne Kind of rocks. Basic par Raúl Baena Martín-Arroyo 1 rocks are formed from molten rocks from the mantle of the Earth . They are classified as volcanic or plutonic . : These are formed when on the Earth ? s surface cools and solidifies . Because this generally happens quickly , volcanic rocks can have a glassy look . Sometimes they trap air bubbles inside , and their are either very small or they don ? t have any at all . : These are formed when lava on the Earth ? s surface cools and solidifies . Because this generally happens quickly , volcanic rocks can have a glassy look . Sometimes they trap air bubbles inside , and their crystals are either very small or they don ? t have any at all .