Rocks formed by the cooling and solidifying of molten materials. Igneous rocks can form beneath the Earth's surface, or at its surface, as lava. if (window.googletag) {googletag.cmd.push(function() { googletag.display('dcomMobileSERPDisplayTopAd-300x250'); });} else {console.error('googletag not defined, dcomMobileSERPDisplayTopAd-300x250');}