Jakob Johannes Sederholm (20 July 1863 – 26 June 1934) was a Finnish petrologist most associated with his studies of migmatites. Troubled by illness throughout his life, Sederholm originally chose to study geology to allow him to work outdoors. After studying first in Helsinki (where he was a student of

Fredrik Johan Wiik Fredrik Johan Wiik, also known as F.J. Wiik, (16 December 1839 in Helsinki – 15 June 1909 in Helsinki) was a Finnish geologist and mineralogist; in 1877, he was named the first professor of geology and mineralogy at the Imperial Alexander Unive ...

), then in

Stockholm Stockholm () is the Capital city, capital and List of urban areas in Sweden by population, largest city of Sweden as well as the List of urban areas in the Nordic countries, largest urban area in Scandinavia. Approximately 980,000 people liv ...

and Heidelberg, Sederholm returned to Finland to work for the Geological Survey of Finland. In 1893 he assumed the role of director of this institution, a post he occupied until his death forty years later. Working on local

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

basement rock In geology, basement and crystalline basement are crystalline rocks lying above the mantle and beneath all other rocks and sediments. They are sometimes exposed at the surface, but often they are buried under miles of rock and sediment. The baseme ...

s, Sederholm instigated a map-making programme that, between 1899 and 1925, published many maps and descriptions of their geological history. Gneisses in the areas he studied (the so-called

Baltic Shield The Baltic Shield (or Fennoscandian Shield) is a segment of the Earth's crust belonging to the East European Craton, representing a large part of Fennoscandia, northwestern Russia and the northern Baltic Sea. It is composed mostly of Archean and ...

) were often of mixed composition, with layers of granitic rock being interleaved with metamorphic rock. Sederholm termed these as migmatites, and viewed them as the product of the

intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

of igneous magma into metamorphic rocks at depth. During his career Sederholm received both the Murchison Medal from the Geological Society of London (1928) and the Penrose Medal from the Geological Society of America (also 1928). The mineral sederholmite is named in his honour. Aside from his geological work, Sederholm was a member of the Diet of Finland, and undertook missions from this to the League of Nations. He was also a member and

chairman The chairperson, also chairman, chairwoman or chair, is the presiding officer of an organized group such as a board, committee, or deliberative assembly. The person holding the office, who is typically elected or appointed by members of the grou ...

(twice) of the Economic Society of Finland. In the 1974

historical novel Historical fiction is a literary genre in which the plot takes place in a setting related to the past events, but is fictional. Although the term is commonly used as a synonym for historical fiction literature, it can also be applied to other ty ...

'' Centennial'', James Michener listed Sederholm among those scientists who made early estimates of the

age of the Earth The age of Earth is estimated to be 4.54 ± 0.05 billion years This age may represent the age of Earth's accretion, or core formation, or of the material from which Earth formed. This dating is based on evidence from radiometric age-dating of ...

. Sederholm's estimate was 40 million years.

Papers

* ''Hackman V.'
Jacob Johannes Sederholm
Biographic notes and bibliography // Bulletin de la Commission géologique de Finlande. 1935. N 112. 34 p. * ''Papunen H.'
Jakob Johannes Sederholm – geologi, humanisti ja totuudenetsijä
// Geologi. 2009. N 2. P. 35-38.

References

Mindat.org Mindat.org is a non-commercial online database, claiming to be the largest mineral database and mineralogy, mineralogical reference website on the Internet. It is used by professional mineralogists, geologists, and amateur mineral collecting, mi ...

)
Sederholmite mineral data
(WebMineral.com) 1863 births 1934 deaths Finnish geologists Petrologists Penrose Medal winners Members of the Royal Society of Sciences in Uppsala {{geoscientist-stub

Papers

References

External links