What are igneous rocks formed by?
Igneous rocks are formed by the direct crystallization of magma into a rock. So any volcano will produce an igneous rock when magma comes out (at which point it is called lava on extrusion). Sedimentary rocks form from weathering, erosion, deposition and compaction of other all three types of rock Metamorphic rocks form from heat and pressure changing (morphing) the crystalline structure of the minerals of a rock into a new rock.
