Leonhard, Karl Cäsar von

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Leonhard, Karl Cäsar von

(b. Rumpenheimbei Hanau, Germany, 12 September 1779; d. Heidelberg, Germany, 23 January 1862),

mineralogy, geology.

Early in his career, Leonhard adhered to the teachings of Werner but later deserted neptunism for volcanism. As the founding editor of the Taschenbuch für die gesammte Mineralogie, Leonhard earned a place among the foremost mineralogists of his time. His prolific writings contributed to the rise of popular interest in geology during the nineteenth century.

In 1797 Leonhard attended the University of Marburg; and in 1798 he went to the University of Göttingen, where his interest in mineralogy was awakened by Johann Friedrich Blumenbach. Because of his early marriage, however, he had to abandon his original intention to study mineralogy under Werner at Freiberg, and he took a position as an assessor in the Bureau of land taxes in Hanau. Nevertheless, he corresponded with Werner, Voigt, and von Buch at Freiberg concerning geology and mineralogy, and he devoted his spare time to pursuing these studies. Beginning in 1803 he traveled frequently through Thuringen and Saxony to study the geology of these areas. From 1805 to 1810 he published his three-volume Handbuch einer allgemeinentopographischen Mineralogie, in which he took Werner’s position on neptunism. Despite the Napoleonic campaigns of this period, Leonhard visited the Austrian Alps and the Salzkammergut, meeting Friedrich Mohs in Vienna and von Moll in Muncih. In 1806 he collaborated with K. F. Marx and H. Kopp on Systematisch tabellrische Übersicht und charakteristik der Mineralien, and in 1807 he originated the Taschenbuch für die gesammte Mineralogie. This journal soon attained prominence and received widespread support from German scientists, and it made Leonhard’s name known throughout Europe. In 1830 the name of the journal was changed to the Jahrbuch für Mneralogie, Geognosie, Geologie und Petrefaktenkunde, and from 1833 to 1862 itRepertorium der appeared as the Neues Jahrbuch für Mineralogie, Geognosie, Geologie und Petrekfaktenkunde. It remains one of the foremost German scientific journals. From 1811 to 1821 Leonhard also edited the Allgemeines Repertorium der Mineralogie.

In 1809 Leonhard became a counselor and adviser in the bureau of mines of the Grand Duchy of Frankfurt, and in 1811 he was appointed the chief of land administration for his regime. In 1813 he was named inspector general and privy councillor of this portion of Napoleon’s Confederation of the Rhine. Considered to be a friend of the French, Leonhard was stripped of his offices after the restoration and was forced t take another position as assessor. In 1815, however, he was called to Munich to teach in the academy, and in 1818 he was appointed professor of mineralogy at the University of Heidelberg, a position he held until his death. In an article concerning the instruction of science and medicine at Heidelberg, which appeared in Christian Karl André’s Hesperus in 1831, Leonhard was described as having an astonishing fund of information concerning minerals and fossils and their classification. The article complained, however, that his approach was completely practical, that his knowledge was limited to the physical properties of minerals, that he completely neglected mathematics and chemistry, and that he used barbaric terminology in his lectures and gesticulated endlessly.

In 1817 Leonhard, together with J. K. Kopp and K. L. Gärtner. published Propädeutik der Mineralogie, considered at the time the most instructive source work in mineralogy. In 1818 he wrote Zu Werners Andenken as a tribute to his old friend: but that same year he also published Zur Naturgeschichte der Vulkane, in which he announced his change of allegiance from neptunism to volcanism because of the increasing evidence forthcoming from the study of basalt.

Leonhard’s Charakteristik der Felsarten (1823) was the most complete work on petrology that appeared in the early nineteenth century. Although written primarily from a mineralogical point of view, the work also contained information concerning the occurrence of various kinds of rocks. Leonhard attempted to divide rocks into four classes: (1) rocks composed of unlike constituents: (2) rocks that are apparently uniform: (3) derivative or fragmented rocks: and (4) friable rocks. He based these distinctions on visible and to a large extent unsatisfactory.

Leonhard’s travels in Auvergne Bohemia, and other volcanic areas, resulted inDie Hüttenerzeugnisse in Die Basaltgebilde (1832). This work was a comprehensive study and conclusively proved the volcanic origin of basalt both with respect to its geological occurrence and to the appearance of the areas where the basalt contacted other rocks. The book aided substantially in the victory of volcanism.

Beginning in 1833 Leonhard turned his attention to the popularization of mineralogy and geology. His first effort, published that year, was Geologie oder Naturgeschichte der Erde, and in 1845-1847 he produced a three-volume work entitled Taschenbuch für Freunde der Geologie and, in 1846, Naturgeschichte des Steinreichs. His last scientific work, Die Hüttenerzeugnisse als Stützpunkte geologischer Hypothesen, appeared in 1858.

Leonhardite, 2(Ca2Al4Si8O24· 7H2O), an aluminosilicate of calcium, was named in honor of Leonhard by Blum in 1843.


I. Original Works. Leonhard was a prolific writer. His chief works are Handbuch einer allgemeinen topogra phischen Mineralogie, 3 vols. (Frankfurt, 1805-1809); Die Form-Verhältnisse and Grupperungen der Gebirge (Frankfurt, 1812), written with P. E. Jasson; Mineralogische Studien (Nuremberg, 1812), written with C. J. Selb;Propädeutik der Mineralogie (Frankfurt, 1817), written with J. K. Kopp and K. L. Gärtner; Zu Werners Andenken(Frankfurt, 1818); Zur Naturgeschichte der Vulkane (Frankfurt, 1818); Handbuch der Oryktognosie (Heidelberg, 1823);Charakteristik der Oryktognosie (Heidelberg, 1823); Die Naturgeschichte des Mineralreichs (Heidelberg, 1825), 2nd ed. Grundzüge der Geognosie and Geologie (Heidelberg, 1831); Agenda geognostica (Heidelberg, 1829); Die Basaltgebilde (Stuttgart, 1832);Geologie oder Naturgeschichte der Erde, 5 vols. (Heidelberg, 1833); Lehrbuch der Geognosie and Geologie (Heidelberg, 1835); Naturgeschichte des Steinreichs (Heidelberg, 1846); Taschenbuch für Freunde der Geologie, 3 vols, (Heidelberg, 1845-1847); Aus unserer Zeit in meinem Leben, 2 vols. (Stuttgart, 1854-1856); andDie HüttenterZeugnisse als Stützpunkt geologischer Hypothesen (Heidelberg, 1858). Leonhard also published about 30 articles in scientific journals.

II. Secondary Literature. See Allgemeine deutsche Biographie, XVIII (Leipzig, 1883), 308-311; Aus der Geschichte der Universität Heidelberg and ihrer Fakülaten (Heidlberg, 1961); and “Obituary, K. C. von Leonhard,” in American Journal of Science, 2nd ser., 33 (1862), 453.

John G. Burke