A geology word. Igneous rock is rock that was once melted — hot liquid rock, either lava that came out of a volcano, or magma that stayed under the ground — and then cooled down and went hard. That is the whole idea: rock made by fire and cooling. Granite is igneous. So is basalt, the dark rock you see in old lava fields. Textbooks usually teach three rock types together, so students meet this word next to two others: sedimentary (made from layers of sand and mud pressed down) and metamorphic (rock changed by heat and pressure but never fully melted). The line between igneous and metamorphic is where students get confused: metamorphic rock got hot, but not hot enough to become liquid. Igneous rock did become liquid. Outside geology class and science writing, almost nobody says this word. It has no everyday or emotional use — you will not hear someone call a person or a temper 'igneous'. It is almost always in front of 'rock' or 'rocks'. There is no verb and no common noun form; if you want the noun idea you just say 'an igneous rock'.