RAMSDELL, LEWIS STEPHEN

(b. Clinton, Michigan, 4 June 1895; d. Palo Alto, California, 14 June 1975)

mineralogy, crystallography.

Ramsdell, the son of Dwight H. and Phoebe Voorhies Ramsdell, attended the University of Michigan, where he received his bachelor’s degree in 1917, his master’s degree in 1919, and his doctorate in 1925. In 1920 he married Lois Ethel Calkins, who received her bachelor’s degree from Michigan that year. The Ramsdells had two daughters.

From the first. Ramsdell’s primary interest lay in mineralogy, and as the topic for his Ph.D. dissertation, he investigated the crystal structures of certain metallic sulfides and closely related selenides, tellurides, arsenides, and antimonides, to determine the degrees of isomorphism among members of these species. To accomplish this difficult task, Ramsdell applied X-ray diffraction techniques, using apparatus built by the General Electric Company. At that time. X-ray diffraction was a relatively new method of studying minerals, used in very few laboratories in the world. Only a handful of structures were known, but it enabled the investigator to solve the structures of crystals on an atomic scale.

Using X-ray diffraction required great ingenuity and patience. Each practitioner had to devise sample preparation and mounting techniques, to determine optimal exposure intervals (which Ramsdell found to vary between fifteen and forty hours!), and to find reproducible methods of measuring films, which were prone to different amounts of shrinkage. Since structures are not deducible directly from the diffraction pattern, high degrees of both geometrical and physicochemical insight are prerequisites for success. Despite these difficulties, Ramsdell determined the structures of nearly twenty metallic sulfides and related minerals, and classified them into iso-structural groups. In the course of this work he also obtained atomic radii for selenium and tellurium.

Ramsdell was appointed instructor in the department of mineralogy at the University of Michigan when he received his master’s degree in 1919. After receiving his doctorate in 1925, he was appointed an assistant professor in 1926. In 1933 he went to England to learn advanced X-ray diffraction techniques at the University of Manchester. On returning to Michigan he built his own X-ray apparatus, using a resuscitated dental transformer, and began teaching a course in which he ultimately trained generations of students in X-ray crystallography. Ramsdell was appointed associate professor in 1935 and full professor in 1944. His introduction of X-ray theory and practice into the curriculum at the University of Michigan was the outstanding accomplishment of his long career as a teacher.

Ramsdell worked out the crystal structures of numerous particularly difficult mineral species. He acted as an adviser to Newman Thibault, who completed a doctoral thesis on silicon carbide structures in 1943. For the next ten years Ramsdell focused much of his attention on SiC, an artificial abrasive with a simple formula but an endlessly confusing array of crystalline structure types. Two polymorphic forms of SiC, with cubic and hexagonal symmetry, were already known, as were at least four different hexagonal and rhombohedral varieties—named I, II, III, and IV for the order of their discovery. Ramsdell identified several more types of SiC and then realized that they could be arranged in a series with integrally proportional axial ratios, that is, the lengths of the repeating cells making up the different types were integer multiples of the same unit.

Crystallographic structures in which identical two-dimensional sheets or layers are stacked at intervals that are multiples of one another were later named polytypes by Lester Strock. Ramsdell proposed that the polytypes of SiC be renumbered in the order of increasingly larger intervals between layers. Where he found gaps in the series of polytypes, he predicted that additional members, with appropriate stacking intervals, would be found. In due time, many more SiC polytypes were found, including those he predicted, and polytypical behavior was discovered to be common to many mineral species. Ramsdell’s work on polytypism was a contribution of fundamental importance to the knowledge of crystal structure.

Ramsdell also classified some of the manganese oxide minerals on the basis of their crystal structures and minor element compositions. After x-raying more than fifty specimens of black opaque samples called psilomelane and “wad,” he identified them as belonging to six separate species. In 1943, the importance of his research on the manganese oxides was recognized by the naming of a newly characterized dimorph of pyrolusite, MnO₂, “ramsdellite” in his honor.

In 1955, Ramsdell determined the crystal structure of coesite, an artificially created, high-pressure, polymorphic form of silica. This mineral was subsequently discovered in target rocks at meteorite impact sites, where it forms at shock wave pressures in excess of 300 kilobars. It is now used as one of the criteria for identifying impact scars.

Ramsdell was one of the “front five” professors who brought great renown to the department of mineralogy at the University of Michigan. In addition to his research and teaching, Ramsdell wrote a textbook of mineralogy with two of the five, Edward H. Kraus and Walter F. Hunt, and he served for many years as an editor of American Mineralogist, the journal that set high standards for the reporting of mineralogical research results. After a long period of aiding the chief editor, Walter F. Hunt, in an anonymous capacity, Ramsdell was appointed assistant editor (1952–1957) and editor (1957–1961). In 1951 he was appointed chairman of the department of mineralogy, a position he held until he retired from the University of Michigan in 1961. Thereafter, the department of mineralogy merged with geology, a change that had taken place in many other universities. After his retirement, the Ramsdells moved to Palo Alto, California.

BIBLIOGRAPHY

I. Original Works. A list of Ramsdell’s publications appears in a memorial to him written by E. William Heinrich, American Mineralogist, 61 (1976), 532–534. The other chief source of information is the Alumni Records Archives at the University of Michigan.

II. Secondary Literature. No biography of Ramsdell has been written, and there are virtually no sources of information on his life aside from Heinrich’s memorial and the Alumni Records Archives at the University of Michigan.

Ursula B. Marvin