(b. Littau [now Litove], near Olomouc, Czechoslovakia, 19 April 1836; d. Vienna, Austria, 4 May 1927)
Tschermak grew up in the small Moravian town in which his grandfather had been a teacher and his father, Ignaz Czermak, was a tax collector. Despite the spelling of their name, the family considered themselves German. Tschermak began his secondary studies with a private tutor, then in 1850 entered Olomouc Gymnasium. He found the German-language instruction there to be inadequate, and this, together with his reaction to the rising tide of Czech national consciousness that followed the revolution of 1848 in Bohemia and Moravia, intensified his own feeling of Germanness and led him to found an anti-Slavic German student union. At the same time, he Germanized the spelling of his name. He distinguished himself in science during these years, and also founded a student natural history club. He was encouraged in these interests by one of his teachers, a Dr. Schwippel, and by the astronomer Julius Schmidt, who was then working in the private observatory in Olomouc.
In 1856 Tschermak enrolled in the Faculty of Philosophy of the University of Vienna. He began to study chemistry with Joseph Redtenbacher and learned the techniques of morphological and optical crystallography from Wilhelm Joseph Grailich. Although he attended no mineralogy lectures, he frequently visited the excellent imperial mineral collection. His first petrological work, “Das Trachytgebirge bei Banow,” was published in 1858, while he was still a student. In 1860 Tschermak passed his teacher’s examinations and was appointed assistant by the mineralogy professor Franz Xaver Zippe; he received the doctorate from the University of Tübingen later in the same year, and in 1861 qualified as Privatdozent in chemistry and mineralogy at the University of Vienna. In 1862 he became second assistant curator of the imperial mineralogical collection, and a few years later, first assistant curator.
During the 1860’s Tschermak began the series of petrographical researches that, with his later work on meteorites, were to bring him an international reputation. He investigated the paragenesis of minerals in several granites, the quartz content in plagioclase, and the role of olivine in various rocks. He also conotributed to the newly emerging methodology of microscopic investigation of rocks by means of using pleochroism to distinguish minerals of the augite, amphibole, and biotite groups. Dissatisfied with current knowledge about the most important rock-forming minerals, he set out to ascertain their crystal forms, their physical properties, and their compositional variations. He was thereby able to present the relationship between these mineral groups and to establish the prerequisites for an exact systematics, to which his chemical analysis of minerals, conducted with his friend Ernst Ludwig, was of fundamental importance.
Tschermak’s most significant contribution in this direction lay in his work on feldspar. He realized that the many varieties of this mineral that had previously been distinguished could be derived from three compounds (which also occur in nature in almost pure form)–potash feldspar, albite, and anorthite. From this he was able to demonstrate that the various calcium-sodium feldspars form a homogeneous isomorphous series from pure calcium to pure sodium feldspar, of which the physical properties are a function of the proportion of the end members, that is, albite and anorthite.
Tschermak published his feldspar theory in Die Feldspatgruppe (1864), a work by which he, after a long dispute, firmly established his point of view. He made this theory the basis for his subsequent research, investigating almost all the important rock-forming silicates to confirm his idea that the great variety of chemical composition demonstrated in this group may be explained by the isomorphic mixture of simple compounds, from which changes in physical properties emerge naturally and in obedience to a law. A further petrographical book, Die Porphyrgesteine Österreichs aus der mittleren geologischen Epoche, embodying his previous research and the results of extensive investigatory travels, won a prize from the Vienna Academy of Sciences in 1867 and was published as a book two years later.
In spring 1868 Tschermak was named associate professor of petrography at the University of Vienna, and in the autumn of the same year he was made director of the imperial mineral collection. He carried on an active research program, which attracted a number of young scientists, and, in order to make their results more widely known, founded the Mineralogische Mitteilungen, of which the first volume appeared in 1871. This periodical soon attracted foreign contributors; its first numbers were published as supplements to the Jahrbuch der K. K. geologischen Reichsanstalt, but after 1878 it was issued independently as Tschermaks mineralogiche und petrographische Mitteilungen.
Tschermak began his work on meteorites in 1870, investigating the mineral content and inner structure of specimens from the imperial collection. He presented a theory of the origin of meteorites whereby these objects were cast off from small celestial bodies by volcanic activity–or, more precisely, by explosions of gases. In 1883 he published Die mikroskopische Beschaffenheit der Meteoriten, which became a standard work on the subject.
During this period Tschermak’s academic career also advanced. In 1873 he was made full professor of mineralogy and petrography at the university (while retaining his curatorial post); in 1876 he received an offer, which he declined, from the University of Göttingen; and in 1877 he gave up his directorship of the imperial collection to devote all of his time of his work at the university where, the following year, a mineralogy and petrology institute was put at his disposal. He was elected dean of the Faculty of Philosophy in 1883 and rector of the university ten years later. He also continued to do research on silicates and meteorites, supplementing it with other petrological and mineralogical works, until his retirement in 1906. His Lehrbuch der Mineralogie was published in 1883, and went through a number of editions, while in 1907, after he had left the university, he was able to demonstrate that certain periodic meteor showers are characterized by petrographical conformity.
Tschermak’s works brought him many honors. He became a member of the Vienna Academy of Sciences in 1875, was awarded the title “Hofrat” in 1886, and, on his retirement in 1906, was ennobled (subsequently styling himself “Tschermak von Seysenegg”). He was one of the founders of the Austrian Mineralogical Society and was elected its honorary president in 1910, on the occasion of the fiftieth anniversary of his doctorate. He was either a member or an honorary member of almost every important scientific society and natural history association. Of the four children of his two marriages, one daughter and two sons became distinguished scientists.
I. Originakl Works. Tschermak’s writings include “Das Trachtgebirge bei Banow,” in Jahrbuch der Kaiserlichen Königlichen geologischen Reichsanstalt, 9 (1858), 63–79; Ein Beitrag zur Bildungsgeschichte der Mandelsteine (Vienna, 1863); Chemisch-mineralogische Studien. I, Die Feldspatgruppe (Vienna, 1864); Beobachtungen über die Verbreitung des Olivins in den Felsarten (Vienna, 1867); Quarführende Plagioklasge steine (Vienna, 1867); Die Porphygesteine Österreichs aus der mittleren geologishen Epoche (Vienna, 1869); Beitrag zur Kenntnis der Salzlager (Vienna, 1871); Ein Meteoreisen aus der Wüste Atacama (Vienna, 1871); Die Bildung der Meteoriten und der Vulkanismus (Vienna, 1875); Die Glimmergruppe (Vienna, 1877); Die mikroskopische Beschaffenheit der Meteoriten (Vienna, 1883); Die Skapolithreihe (Vienna, 1883); and Lehrbuch der Mineralogie (Vienna, 1884).
In addition to memoirs in Mineralogische und petrographische Mitteilungen, Tschermak published articles in Justus Liebigs Annalen der Chemie, Neues Jahrbuch für Mineralogie, Geologie und Paläontologie, Poggendorff’s Annalen der Physik und Chemie, Almanach der Akademie der Wissenschaften in Wien, Denkschriften der Akademie der Wissenschaften (Vienna), and Sitzungsberichte der Akademie der Wissenschaften in Wien.
II. Secondary Literrature. The most extensive obituary is by Tschermak’s student and successor as professor, Friedrich Becke, in Mineralogische und petrographische Mitteilungen, 39 (1928), i-x. Other obtiuaries are by E. S. Dana, in American Journal of Science, 5th ser., 14 (1927), also in American Mineralogist, 12 (1927); and by J. W. Evans, in Nature, 120 (1927), 195–196. Mineralogische und petrographische Mitteilungen. 25 (1906), dedicated to Tschermak on his retirement, contains a signed photographic potrait.