Dieudonné Sylvain Guy Tancrède de Gratet de Dolomieu usually known as Déodat de Dolomieu (; 23 June 175028 November 1801) was a French geologist. The mineral and the rock dolomite and the largest summital crater on the Piton de la Fournaise volcano were named after him. Biography Déodat de Dolomieu was born in Dauphiné, France, one of 11 children of Marie-Françoise de Berénger and her husband, the Marquis de Dolomieu. As a child young Déodat showed considerable intellectual potential and special interest in the natural surroundings of his home in the Alps of southeastern France. De Dolomieu began his military career in the Sovereign and Military Order of the Knights of Saint John (also called the Knights Hospitaller or the Knights of Malta) at the age of 12. His association with the Maltese order caused him difficulties throughout his life, beginning with a duel, which he fought at the age of 18, when he killed a fellow member of the order. For this infraction he was sentenced to life in prison but due to the intercession of Pope Clement XIII he was released after only one year. Career During the years prior to the French Revolution Dolomieu took full part in the intellectual ferment of France and the rest of Europe. He maintained numerous social contacts among the nobility and although he never married, Dolomieu had something of a reputation as a ladies' man. Through his friend and mentor, the Duke de La Rochefoucauld, Dolomieu was made a corresponding member of the Royal Academy of Sciences. He spent his spare time taking scientific excursions throughout Europe collecting mineral specimens and visiting mining areas. His particular interests included mineralogy, volcanology, and the origin of mountain ranges. Although Dolomieu was greatly interested in volcanoes, he became convinced that water played a major role in shaping the surface of the Earth through a series of prehistoric, catastrophic events. Dolomieu was not a uniformitarian geologist. He has been described as a "non-actualistic catastrophist". His contemporary, James Hutton, did not publish the principle of uniformitarianism until 1795. Dolomieu was an observationalist and spent much of his time collecting and categorizing geological data. Unlike Hutton, no scientific principles or theories are credited to him, although he left his permanent mark on geology in another way: that is by discovering the mineral dolomite that would be named after him. Geology of the Dolomites During one of his