Sources of igneous rock are formed from magmas, which are molten rocks that originate from the Earth's mantle. Magmas are composed of minerals and dissolved gases and are created by the melting of rocks due to high temperatures and pressures. Magmas can be found in volcanoes, mid-ocean ridges, and hotspots. When magmas cool and solidify, they form igneous rocks such as basalt, granite, and pumice.