Compléter Igneous rocksVersion en ligne Igneous rocks 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 . Volcanic : 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 . Plutonic : These are formed when under the Earth ? s surface cools and solidifies . Because this process is slow and happens under a lot of , plutonic rocks often have crystals that are easy to see . These rocks are the most common type found in the Earth ? s . Sedimentary Rocks The sand on a beach , the mud at the bottom of a lake and on a river bank are all sedimentary rocks . These are rocks that have formed from the compaction of , or fragments of older rocks . Metamorphic rocks have been transformed over time by intense and pressure , deep under the ground . Some rocks are formed in sheets or which are generally parallel to each other . This layered form is known as .
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