Guettard, Jean-Etienne (1715–1786)

French naturalist. He pioneered geological mapping and also studied botany and medicine, as well as the origin of various types of rock. Research in the field suggested that the rocks of the Auvergne district of central France were volcanic in nature, and Guettard boldly identified several peaks in the area as extinct volcanoes, though he later had doubts about this hypothesis. Of basalt, he originally took the view that it was not volcanic in origin, but changed his mind after visits to Italy in the 1770s.

Guettard was born in Etampes, Ile-de-France, and became keeper of the natural-history collection of the duc d'Orléans. In 1746 he presented his first mineralogical map of France to the Académie des Sciences; and in 1766, he and chemist Antoine Lavoisier were commissioned to prepare a geological survey of France, though only a fraction was ever completed.