Rhyolite is the most representative rock of the Massif de l'Estérel. This crystalline acid effusive rock of porphyry (volcanic) origin has a composition close to that of granite in the Streckeisen diagram. It owes its characteristic orange-red color to hematite, a mineral with a high content of iron and other minerals such as titanium and manganese, the compounds of which are released and color it in the presence of water.