Igneous rocks are formed by the cooling and hardening of molten rocks. There are two types of Igneous Rocks. Extrusive/Volcanic Rocks. When magma reaches the surface it is called Lava. LAVA cools and hardens to form EXTRUSIVE rocks. When the cooling is very fast (almost instant) it will form rocks without crystals e.g. Obsidian, while if it is not that fast it will form tiny crystals e.g. Basalt. Intrusive/Plutonc Rocks; Magma does not always reach the surface but may solidify below the Earth’s surface. In this case it forms intrusive igneous rocks.
Lecture on Igneous Rocks
