Pierre Armand Dufrenoy, a French geologist and mineralogist, born at Sevran, Seine-et-Oise, in 1792, died in Paris, March 20, 1857. His mother Adelaide (1765-1825) was a poetess of merit. His first essay appeared in 1819, and was followed by a great variety of papers on mineralogy and geology, which gained him a high reputation. His explorations in southern France and in the Pyrenees led him to develop the theory of meta-morphism. He explored the vicinity of Naples, and in his essay entitled Des terrains vol-caniques des environs de Naples he maintains that Herculaneum and Pompeii were destroyed by a landslide from Vesuvius. With Elie de Beaumont he explored between 1823 and 1836 various parts of France, England, and northern Spain, the principal result of which was the great geological map of France, with 3 vols. of text, published in 1841. Another product of their common labors was the Voyage metal-lurgique en Angleterre (2 vols. 8vo, 1827; enlarged ed., 1837-'9). (See Elie de Beaumont.) He was one of the most active members of the academy of miners, director of the school of mines, and professor of mineralogy and geology.

He introduced a new classification of minerals based upon crystallography, promoted in various other ways the study of mineralogy and meteorology, and published a Traite de mineralogie (2d ed., enlarged, 4 vols. 8vo and 1 vol. of plates, Paris, 1856-'9).