
Under the snow and glaciers, two major rocks form the Mont-Blanc Massif: the sharp edges and highest peaks are made of very hard granite (from left to right: Chamonix Needles, including the Aiguille du Midi, Mont Blanc du Tacul, Mont Maudit, Mont Blanc summit), while the rounder, softer parts are made of gneiss (from left to right: Dôme du Goûter, Aiguille du Goûter, Aiguille de Bionnassay....).
These two so-called crystalline rocks come from the Earth's molten core.