Mont Gerbier de Jonc is a mountain of volcanic origin located in the Massif Central in France.

It is made of a type of rock called phonolite.

It rises to an altitude of 1,551 m (5,089 ft), and its base contains three springs that are the source of the Loire, France's longest river.

[citation needed] Mont Gerbier de Jonc was formed 8 million years ago when a volcano erupted molten phonolite lava.

The lava was too viscous to flow far and it cooled to form a lava dome of phonolite rock in the crater of the volcano.