Answer:
Igneous rocks are formed due to volcanic eruption, where molten lava is solidified when it comes on the surface of the earth. Sometimes molten lava gets trap in the crust, which slowly cools along with high pressure, forms granite.
The chemical composition of igneous rocks is mainly silica, iron, aluminium etc. while volatile materials get evaporated like sulphur. They may also contain small traces of radioactive metals like radium, uranium etc. The mineral composition of igneous rocks is feldspar, quartz, hornblende, pyroxene, olivine etc.