The video explains the formation of igneous rocks, both intrusive and extrusive. Intrusive rocks form when magma cools slowly beneath the Earth's surface, allowing large crystals to develop, as seen in pegmatite. In contrast, extrusive rocks form when lava cools quickly on the surface, resulting in smaller crystals, as in rhyolite. Obsidian forms so rapidly that no crystals are visible, giving it a glass-like appearance. Some extrusive rocks, like pumice, have trapped gases that create air pockets, enabling them to float.

What new insight or understanding did you gain from this video?