Friedel, Georges

(b. Mulhouse, France, 19 July 1865; d. Strasbourg, France, 11 December 1933)

crystallograbhy.

Georges Friedel was the son of the famous chemist Charles Friedel (1832–1899), who taught mineralogy and organic chemistry at the University of Paris and was, at the same time, the curator of the mineralogical collections of the School of Mines. Charles’s father was a banker in Strasbourg; his maternal grandfather was Georges Duvernoy, a co-worker of Cuvier and his successor at the Collège de France. The Friedel family had left their Alsatian home before the Franco-Prussian War. Georges spent his childhood, untill the age of fifteen, in Paris, where his parents’ apartment was in the building of the School of Mines. This school was to exert a profound influence on his career. He entered the École Polytechnique in 1885, having placed first in the competitive entrance examination. Upon graduation he returned to the School of Mines for a three-year course (1887–1890). Mallard was his professor of mineralogy, and his father introduced him to research in mineral synthesis. He married Hélène Berger-Levrault (1888) while still in graduate school.

As a mining engineer Friedel received an appointment in the French civil service (1891) and was put in charge of the Moulins district. In 1893 he entered the School of Mines at Saint-Étienne, where he taught courses in assaying, ferrous metallurgy, physics, mineralogy, geology, and the applications of electricity to mining. From 1899 he lectured only on geology and mineralogy, and after he became director (1907), he limited himself to mineralogy. Friedel felt strong ties to the Saint-Étienne school and declined several calls from the School of Mines in Paris. But, after World War I, he did accept the chairmanship of the Institute of Geological Sciences at the newly reopened French University of Strasbourg, where his greatgrandfather Duvernoy had been the dean of the Faculty of Sciences some eighty-five years before. The return to his liberated Alsace was one of the great joys of his life. For some time before his retirement in 1930, a painful illness prevented Friedel from giving his courses, and his son Edmond substituted for him. He was confined to his room, and one of his daughters, Marie, nursed him with great devotion. His wife had died in 1920. Racked with great physical suffering, he kept his intellectual curiosity and marvelous lucidity to the end.

The work of Friedel is remarkable for its diversity. It is essentially crystallographic and mineralogical, but it deals also with petrology, geology, and even engineering and pedagogy.

Jointly with his father, Friedel first published accounts of a number of syntheses produced in a steel tube lined with platinum, at about 500°C. and under high pressure. Synthetic minerals were prepared by letting group I hydroxides and silicates or salt solutions act on mica. Among nonminerals he obtained tricalcium aluminum hexahydroxytrichloride dihydrate (1897) and a calcium aluminate (1903), both known for their twinning, and lithium metasilicate (Li₂SiO₃), which syncrystallizes with beryllium orthosilicate (Be₂SiO₄). With Francois Grandjean, Friedel synthesized chlorites by attacking pyroxene with alkali solutions (1909). By preparing potassium nepheline (1912) he settled the question of “excess silica” in the nepheline formula.

Friedel’s work (1896–1899) established the interstitial nature of zeolitic water, which can be replaced by many liquids and gases in the zeolitic “sponge.” He found zeolitic water in compounds other than zeolites.

In 1893 Friedel developed a method for the accurate measurement of path-difference that is based on the restoration of elliptically polarized light to plane polarized light. This method was later applied to the study of stressed glass by R. W. Goranson and L.H. Adams.

In 1904 the law of Bravais, based as it was on speculative considerations, was far from being generally accepted. Friedel established its validity as a law of observation, regardless of theory. In this sense the law of Bravais is truly Friedel’s: given any crystalline species with sufficient morphological development, it is always possible (and herein lies the law) to find a lattice such that the spacing d(hkl) of a family of parallel nets is, to a first approximation, a measure of the frequency of occurrence of the corresponding form {hkl}. Friedel determined this unique morphological lattice for hundreds of substances, thereby removing the arbitrariness of the unit lengths choesn in accordance with the law of simple indices.

Another empirical law enunciated by Fiedel, and shown by Alfred Liénard to be a consequence of the law of Bravais, is the law of mean indices (1908): the cell edges, a, b, c, are roughly proportional to the sums, Σh, Σk, Σl, of the absolute values of the indices of the observed forms . After 1912, when the structural lattice, which expresses the periodicity of the crystal structure, could be determined by X-ray diffraction, Friedel noted that in many instances it did not coincide with his morphological lattice. This discrepancy, he pointed out, does not diminish but, rather, enhances the value of the morphological lattice, which remains the expression of duly observed facts. Final confirmation of the law of Bravais came with its generalization by J. D. H. Donnay and D. Harker in 1937, after Friedel’s death, when it was found that the effective interplanar spacings depend not only on the lattice mode but also on the glide planes and screw axes in the space group.

In 1905 the Bravais lattice was, structurally speaking, only a hypothesis. Friedel proved its physical reality by noting that irrational threefold axes (compatible with the law of rationality but impossible in a lattice) had never been found in crystals. This fundamental observation is known as Friedel’s law of rational symmetric intercepts.

Bravais and Mallard had begun the theory of twinning. In 1904 Friedel completed it and stated the general law that governs all twins: a lattice, the “twin lattice,” extends through the whole crystalline edifice; it is the crystal lattice itself or one of its superlattices; its prolongation from one of the twinned crystals to another can be exact or approximate. Hence the four possibilities and the classification of twins into four classes. The theory accounted for all known twins but one: the Zinnwald twin in quartz. Friedel’s very last paper (1933), correlating observations of J. Drugman and results of M. Schaskolsky and A. Schubnikow on alum, explains the exception: two pre-existing crystals unite during growth, one face of the smaller adhering to another face of the larger, in such an orientation as to have a lattice row in common. The theory was thus generalized: in addition to the four classes of triperiodic twins, monoperiodic twins, such as the Zinnwald twin, must be recognized; diperiodic ones, in which the twinned crystals would have a net in common (as in epitaxy), should also be possible.

Lehmann’s so-called liquid crystals were thoroughly investigated by Friedel and his co-workers Francois Grandjean, Louis Royer, and his son Edmond from 1907 to 1931. Two new stases (structural types of matter), the nematic and the smectic, were found to exist between the amorphous and the crystalline. (Cholesteric substances belong to the nematic stasis.) The four stases are separated by discontinuous transformations, which justify the classification. A treatment in English is available in J. Alexander’s Colloid Chemistry (1926); it summarizes the detailed review paper of 1922, which to this day remains the indispensable introduction to the field. Friedel’s work on the mesomorphous stases is perhaps the most important of all his contributions: its many new observations and interpretations opened up most of the lines of research now pursued in this field, where it remains the basic reference.

Friedel took an immediate, although theoretical, interest in Laue’s discovery of X-ray diffraction by crystals (1912). As early as 1913 he enumerated the eleven centrosymmetries that can be determined by X rays (Friedel’s law, to X-ray diffractionists). Other papers deal with the role of the length of the X-ray wave train (1913), the calculation of intensities (1919), and diffraction by solid solutions (1926).

Friedel was responsible for a theory of crystal growth (1924–1927) that brings out the similarity of crystal corrosion by a slightly undersaturated solution and crystal growth in a slightly supersaturated one. The two phenomena are symmetrical with respect to the saturation point. The theory thus explains negative crystals. Curved faces are accounted for by convergent and divergent diffusion (angle effect, edge effect).

Friedel pointed out that a holoaxial hemihedry may be simulated by a holohedral crystal grown in an optically active medium. He also studied diamond, clarified its holohedry, discussed its inclusions, ascribed its birefringence to strain, and (with Ribaud, 1924) on rapid heating to 1885°C., found a new allotropic form, still unconfirmed but possibly the “white carbon” described by A. El Goresy and G. Donnay (“A New Allotropic Form of Carbon From the Ries Crater,” in Science, 161 [1968], 363–364).

Friedel’s chief geological contribution was the recognition of the first mylonite in France (with Pierre Termier, 1906). In 1907 he was awarded the Prix Joseph Labbé of the French Academy in recognition of the part he had played in the discovery of a new coalfield.

As a school administrator at Saint-Étienne, Friedel stressed laboratory work and introduced new courses in statistics, foreign languages, economics, and industrial hygiene; at Strasbourg, he planned the scientific training of geological engineers and was one of the founders of the Petroleum Institute. As a teacher he exerted an enormous influence, which is still felt: his admirable textbook Leçons de cristallographie (1926) was reprinted in 1964. Its often quoted preface, entitled “A Warning,” is a sort of scientific testament, stressing the importance of meticulous observation and scrupulous acceptance of well-established facts.

BIBLIOGRAPHY

I. Original Works. For a complete list of Friedel’s works, see Grandjean’s article. Among his writings note especially “Les états mésomorphes de la matière,” in Annales de physique, 18 (1922), 273–474; “The Mesomorphic States of Matter,” in J. Alexander, Colloid Chemistry, I (New York, 1926), 102–136; and Leçons de cristallographie professées à la Faculté des sciences de Strasbourg (Paris, 1926; repr. 1964).

II. Secondary Literature. On Friedel or his work, see J. D. H. Donnay, “Memorial of Georges Friedel,” in American Mineralogist, 19 (1934), 329–335, with condensed bibliography; F. Grandjean, “Georges Friedel 1865–1933,” in Bulletin de la Société française de minéralogie,57 (1934), 144–171, with bibliography, 172–183; Memorial Volume, Georges Friedel 1865–1933 (Strasbourg-Paris, 1939), a limited ed. of 1,000 numbered copies; and A. F. Rogers, “Friedel’s Law of Rational Symmetric Intercepts, Withy Bibliography of Irrational Three-Fold Axes of Symmetry,” in American Mineralogist, 10 (1925), 181–187.

J. D. H. Donnay