(b. Saint-Quentin, France, 24 April 1796; d. Paris, France, 13 October 1878)
The son of a provincial magistrate, Delafosse graduated from schools in Saint-Quentin and Rheims and became a scholarship student at the École Normal Supérieure. Upon completion of his studies there in 1816, he went to work for Haüy, whose mineralogy courses he had attended at the Muséum d’Histoire Naturelle. He assisted Haiiy in editing and publishing Traité de CristalloGraphie(1822) and the posthumous last three volumes of the second edition of theTraité de minéraiogie(1822-1823). Delafosse’s appointment as assistant naturalist in 1817 began his lifelong association with the Muséum, where he became a professor in 1857, replacing Dufrénoy. He was also associated with the Paris Faculté des Sciences from 1822, obtaining a professorship of mineralogy in 1841, as successor to Beudant. For many years he taught at the École Normale Supérieure (1826- 1857). His election to the section of mineralogy in the Academie des Sciences occurred in 1857. He was a founding member of the Société Geologique de France.
As Haüy’s pupil, Delafosse was a member of the second generation of the creators of modern crystallography. Like his teacher he was guided by a deep commitment to symmetry as the basic principle for the investigation of crystals. Unlike Haüy, however, Delafosse distinguished clearly between the integrant or subtractive molecule, a geometrical invention, and the chemical molecule, without discarding the belief that a crystal’s exterior symmetry must be governed by the internal symmetry of the molecular arrangement. Haüy’s subtractive molecule might then correspond to groups of several chemical molecules, and cleavage would proceed by cutting through subtractive molecules (instead of through the interstices between them) and along networks of chemical molecules forming a surface. By this means Delafosse was able to bring hemihedral properties of crystals into accord with crystallographic theory. In modern terminology the hemihedralism was ascribed to a geometric polarity of the chemical molecule.
Seeking to relate the structure and chemical composition of crystals, Delafosse investigated plesiomorphism, or similarity in crystal form unaccompanied by chemical identity. His method of mineral classification was based on both chemical composition and crystal form. He also studied relations between the morphology of crystals and their physical properties, such as electricity, light, and heat. Among his students who extended such studies fruitfully was Louis Pasteur.
I. Original Works. Delafosse’s most comprehensive work was Nouveau cours de minéralogie comprenant la description de toutes les espèces minérales avec leurs applications directes aux arts, 3 vols, and atlas (Paris, 1858-1862), drawn from his courses at the École Normale, the Muséum, and the Sorbonne, and published after he had attained recognition as a major figure in mineralogy. His doctorol dissertation at the Paris Faculté des Sciences, De la structure des cristaux considérée comme base de la distinction et de la cristaux considérée comme base de la distinction et de la classification des systèmes cristallins (Paris, 1840), set forth his theory of crystal structure. He linked the form and physical properties of crystals in “Recherches sur la cristallisation, considérée sous les rapports physiques et mathematiques,” in Mémoires présentées par divers savants à l’Académie royale des sciences de l’Institut de France.8 (1843), 641-690; chemical composition was related to crystal morphology in “Mémoire sur une relation importante qui se manifeste, en certains cas, entre la composition atomique et la forme cristallinc. et sur line nouvelle application du rôle que joue la silice dans les combinaisons minérales,” ibid.,13 (1852), 542-579.
His Mémoire sur le plésiomorphisme des espèces minérales (Paris, 1851) was extracted in Comptes rendus de l’Académie des sciences,32 (1851), 535-539, as were his “Mémoire sur la structure des cristaux et ses rapports avec les propriétés physiques et chimiques,” 43 (1856), 958-962, and “Sur la véritable nature de l’hémiédrie et sur ses rapports avec les propriétés physiques des cristaux,” 44 (1857), 229-233. Earlier articles include “Observations sur la méthode générale du Rév.W. Whewell pour calculer les angles des cristaux,” in Annales des sciences naturelles,6 (1825), 121-126; and “Mémoire sur l’électricité des minéraux,” in Annales des mines,3 (1818), 209-226.
Delafosse contributed articles to Charles d’ Orbigny’s Dictionnaire universel d’histoire naturelle, 13 vols, and atlas in 3 vols. (Paris, 1841-1849), of which he was an editor. He was one of the principal editors of Baron de Férussac’s Bulletin des sciences naturelles et de géologie (1824-1831), a section of Bulletin universel des sciences et de l’industrie. He prepared a review of the development of mineralogy in France during this time: Rapport sur les progrès de la minéralogie (Paris, 1867).
In accord with his deep interest in teaching, Delafosse published a number of didactic works in science, including Précis élémentaire d’histoire naturalle, à l’usuage des collèges et des maisons d’ éducation, 4 vols. (Paris, 1830), republished in many subsequent eds.; Notions élémentaires d’histoire naturelle, 3 vols. (Paris 1835-1836), also republished many times; and Lecons d’histoire naturelle (Paris, 1838).
Delafosse also prepared a Notice sur les travaux scientifiques de M. Delafosse (Paris, 1851).
II. Secondary Literature. There is no biography of Delafosse. Biographical information comes mainly from such contemporary eulogies as Ch[arles] Friedel, “La vie et les travaux de Delafosse,” in Revue scientifique,no. 21 (1878), 481-484; Ed[mond] Hébert, Notice sur Gabriel Delafosse (Versailles, 1879), extracted from Compte rendu annuel de l’Association des anciens élèves de l’École normale and based largely on Friedel’s sketch; Edourad Jannettaz, “Notice nécrologique sur M.G. Delafosse,” in Bulletin de la Société géologique de France, ser, 3,7 (1878-1879), 524-530; A.L.O. Legrand Des Cloizeaux’s note on Delafosse in Comptes rendus de l’Académie des sciences,87 (1878), 569-570; and an unsigned biographical sketch in l’ Année scientifique et industrielle,22 (1878), 494-495.
Kenneth L. Taylor