[en] This book reports a journalist's inquiry of what is behind the search for and exploitation of some specific metals, and more particularly rare earth metals which are present in many new technologies which are supposed to protect us against pollutions, or to favour energy transition. The author shows that the extraction of these metals requires huge amounts of energy, and also generates pollution, and are therefore not that much promoters of energy transition nor of the protection of the environment, as for example in some African countries and more particularly in China which is the main world producer of germanium (present in solar arrays), of vanadium (aerospace industry) and of rare earths. As they are present is so many devices, these materials represent a critical economic and geopolitical issue