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Karl Cäsar von Leonhard

Karl Cäsar von Leonhard was born in Rumpenheim bei Hanau, Germany on September 12, 1779, the son of Katharine Suzanne Godeffroy and Johann Konrad Leonhard (an administrator in the service of Count Karl of Hessen). He and attended the University of Marburg in 1797, then moved on to the University of Göttingen in 1798. There he acquired an interest in minerals from his mineralogy professor, Johann Friedrich Blumenbach (1752-1840). He had planned to go on to study mineralogy under Abraham Werner in Freiberg, but an early marriage in 1802 (to Marie Louise Wilhelmine Blum, eldest daughter of a financier in Hanau) brought financial responsibilities that forced him to leave school and take a job as an assessor in the Bureau of Land Taxes in Hanau. Nevertheless he carried on a correspondence with Werner and other professors in Freiberg, and studied mineralogy on his own in his spare time.

In 1803 Leonhard began making frequent mineral collecting trips throughout Thuringia and Saxony. He probably accumulated more specimens than he ultimately needed, and so was inspired to begin selling some of them on the side; in 1804 he established a part-time mineral business. During the next few years he toured the Austrian Alps, meeting Friedrich Mohs in Vienna and Baron Karl von Moll in Munich.

In 1806 Leonard, in collaboration with Ernst K. F. Merz and Johann Heinrich Kopp, published Systematisch tabellarische Übersicht und Charakteristik der Mineralien ("Systematic tabulated overview of the properties of minerals"), and in 1807 he founded a magazine specifically for mineralogists and mineral collectors, called Taschenbuch für die gesammte Mineralogie ("Notebook for the whole of mineralogy"). The journal soon became popular and gained the support of mineralogists across Europe, making Leonhard's name widely known. (In 1830 the name of the journal was changed to Neues Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefakenkunde; it remains a prestigious mineralogical journal today.)

From 1805 to 1809 Leonhard published his three-volume Handbuch einer allgemeinen topographischen Mineralogie, one of his major works. From 1811 to 1822 he also served as editor of the journal Allgemeines Repertorium der Mineralogie. He held various other jobs from 1809 to 1818, when he returned to Heidelberg to accept the position of Professor of Mineralogy at the University of Heidelberg, where he remained for the rest of his life.

Leonhard had an extensive practical knowledge of the physical properties of minerals and fossils, but because of his abbreviated education his lectures completely neglected the chemical and mathematical aspects of mineralogy. He is said to have used "barbaric terminology in his lectures and gesticulated endlessly."

In 1817 Leonhard, with his friends J. K. Kopp and K. L. Gärtner, published Propädeutik der Mineralogie ("Introduction to Mineralogy"), a valuable and instructive compendium of all sorts of information useful to the mineralogist and mineral collector. His Charakteristik der Felsarten (1823) was the most comprehensive work on petrology to appear in the early 19th century, but, being based solely on visual examination, it was arbitrary and largely unsatisfactory by modern standards.

After operating his part-time mineral business intermittently for 20 years without help, Leonhard finally turned proprietorship over to a young mineralogist, Friedrich Moldenhauer, in 1824. But Leonhard continued to be involved in the business, probably as owner and certainly as advisor. They named the company the Heidelberger Mineralien-Comptoir. Johann Wolfgang von Goethe (1749-1832) was one of Leonhard's customers, specimen suppliers and regular correspondents (beginning in 1807); Goethe wrote a friendly letter to Leonhard on February 3, 1826, saying: "How much my cabinet owes overall to your sympathetic consideration." Apparently Goethe also acted as an intermediary for Leonhard in specimen trades. On February 25, 1826, Goethe remarked: "I know quite well that bartering, particularly in this subject [minerals], has difficulties, because each party values his supply probably more highly than the other one." And on September 3, 1826, Goethe wrote: "You will receive by the next post a small packing case of minerals…"

Moldenhauer left in 1828, and Leonhard sought to keep the Heidelberger Mineralien-Comptoir going with the help of his friend, Heinrich Georg Bronn (1800-1862), his co-editor of Neues Jahrbuch für Mineralogie. In an ad in the Magazin für Pharmacie for February 1828 the Heidelberger Mineralien-Comptoir (Leonhard still declined to attach his own name to any advertisements) offered a number of "Collections of Minerals, Fossils and Crystal Models," including (1) an oryktognostic collection of 650 mineral specimens organized according to Leonhard's Handbuch der Mineralogie, (2) a gemstone collection of 50 pieces, (3) a geognostic collection of 600 specimens, (4) a pharmaceutical collection of minerals, (5) a collection of 700 minerals of economic value, (6) a fossil collection, and (7) a collection of 123 crystal models. The ad pointed out that "Every specimen comes with a label (available in French, German or English) giving the species name and the locality."

Leonhard and Bronn continued to operate the business for several years following the departure of Moldenhauer. Even though Leonhard meticulously kept his name out of advertisements, everyone knew it was his company. At the September 12, 1834 meeting of the Congres Scientifique de France, the moderator, Mr. Desvaux, brought to the attention of the attendees: "… the catalog of the Comptoir Mineralogique et Geologique very recently founded in Paris, like that which the Baron Mr. Leonhard directs in Heidelberg."

In 1833 Leonhard turned his attention again toward popularizing mineralogy and geology, with the publication of his Geologie, oder Naturgeschichte der Erde ("Geology, or a Natural History of the Earth"). His personal bibliography lists numerous other works, including 30 articles in scientific journals.

In 1841 Leonhard brought in a young mineralogist, J. Lommel, to run the Heidelberger Mineralien-Comptoir. Lommel inherited the business when Leonhard died on January 23, 1862. After Lommel's death in 1868 it was taken over by L. and Daniel Blatz; by 1920 it had passed to the management of Friedrich Rodrian.

Leonhard built a huge personal mineral collection of 8,000-10,000 specimens, bequeathed to the University of Göttingen upon his death. The mineral leonhardite was named in his honor by Johann Reinhard Blum (1802-1883) in 1843, but it was later discredited as dehydrated laumontite. ____________________________________

BESNARD, A. F. (1870) Necrologie. [Obituary notice for J. Lommel] Correspondenz-Blatt des Zoologisch-Mineralogischen Vereines in Regensburg, 24 (2-3), 39.
BURKE, J. G. (1973) Karl Cäsar von Leonhard, in Dictionary of Scientific Biography, vol. 8, p. 245-246.
DEUTSCHE APOTHEKER BIOGRAPHIE (1986) Moldenhauer, Friedrich, Supplement 1, 319-320.
GOETHE, J. W. von (1816-1828) Letters; available online from
GOLDSCHMIDT, V., and THOMSON, E. (1920) Tetragonal system: Phosgenite from Tsumeb, Ambo-Land, Southwest Africa. American Mineralogist, 5 (7), 131-133.
HAAST, J. (1881) Origin and early history of the Canterbury Museum. Transactions and Proceedings of the Royal Societyof New Zealand, 14, 503-504.
HAMILTON, W. J. (1860) [quoted in] Geological and Mineralogical Collections. Nelson Examiner and New Zealand Chronicle, 19 (34), 2.
KIRCHHEIMER, F. (1969) Heidelberg und der Löss. Ruperto-Carola: Zeitschrift der Vereinigung der Freunde Studentenschaft der Universität Heidelberg 46, 3–7.
SMALLEY, I. J., JEFFERSON, I. F., DIJKSTRA, T. A., and DERBYSHIRE, E. (2001) Some major events in the development of the scientific study of loess. Earth-Science Reviews, 54, 5-18.
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