philosopher's stone
From Longman Dictionary of Contemporary Englishphilosopher's stonephiˌlosopher’s ˈstone noun [singular] RPan imaginary substance that was thought in the past to have the power to change any other metal into goldExamples from the Corpusphilosopher's stone• All that is needed is for the philosopher's stone of artistic intention to be applied to them.• There is more than a hint of the search for the philosopher's stone.