Igneous rock is formed whenever any type of molten rock cools down and solidifies. Igneous rock needs ignition – it has to be so hot that it turns into a liquid or semi-liquid before cooling and solidifying.
Think of a volcano that starts to erupt after an ignition key is turned. The magma that stays below the earth’s surface, and the lava that pours out, cool to become igneous rock.
Granite, basalt and pumice are examples of igneous rock.
To help you recall this, imagine a gran who knits (granite). She is in a bath on a sea of lava, with a pumice stone and bath salts (basalt) on the side of the bath.