FRIEDEL, GEORGES

born July 19, 1865, Mulhouse, Fr. died Dec. 11, 1933, Strasbourg French crystallographer who formulated basic laws concerning the external morphology and internal structure of crystals. Friedel studied at the cole Polytechnique and the Superior National School of Mines, where his father, the chemist Charles Friedel, was curator of the mineralogical collections. After graduation he worked as a mining engineer and then turned to teaching and research, first at the School of Mines of Saint-tienne and later at the University of Strasbourg. Friedel's observations established the general validity of the hypothesis, put forward by Auguste Bravais, that the different faces of crystals were external expressions of a periodic, internal arrangement of atoms, or lattice structure. His own law of rational symmetric intercepts (1905) and law of mean indices (1908) are generalizations of the regularities observed in the external symmetry of crystals. After conclusive proof of the lattice structure was achieved in 1912 by the X-ray diffraction experiments of Max von Laue, Friedel showed that, because the X-ray diffraction pattern is always symmetric, it is impossible (except under special circumstances) to determine whether the crystal actually has a centre of symmetry and that only 11 different types of crystal symmetry can be distinguished. This result is known as Friedel's law, and the 11 possible types of symmetry are known as Friedel classes (or Laue symmetry groups).