FAMOUS GEOLOGISTS Victor Moritz Goldschmidt (1888–1947) – Mineralogist and Geochemist Victor Goldschmidt is considered, with the Russian Vladimir Vernadsky, as the founder of modern geochemistry and crystal chemistry. He developed what is now known as the Goldschmidt Classification of Elements. Goldschmidt was born in Zürich, Switzerland but the family moved to Norway in 1901 when his father, Heinrich Goldschmidt became Professor of Chemistry in the University of Kristiania (Oslo). Victor Goldschmidt was awarded a post-doctoral fellowship from the university at the age of 21 and soon published two major works, his doctoral thesis on ‘The Contact Metamorphism of the Kristiania District’ (1911) [Die Kontaktmetamorphose im Kristianiagebiet] and ‘Geological and Petrographic Studies in the Highlands of Southern Norway’ (1912) [Geologisch-petrographische Studien im Hochgebirge des südlichen Norwegens]. In 1912 Goldschmidt was made Associate Professor of Mineralogy and Petrography and in 1914 applied for a professorship in Stockholm. Before his appointment could be ratified the University of Kristiania offered him a similar chair. Goldschmidt commenced a series of 8 volumes in 1923 under the title ‘Geochemical Laws of the Distribution of the Elements’ [Geochemische Verteilungsgesetze der Elemente], the start of his research in geochemistry. In this work he coined the term ‘lanthanide contraction’, the greater than expected decrease in ionic radii of elements in the lanthanide series from atomic number 57 (lanthanum) to 71 (lutetium) which results in smaller than might be expected ionic radii for the subsequent elements starting with 72 (hafnium). The Goldschmidt Classification The Goldschmidt Classification (image 1) groups the chemical elements according to their preferred host phases into lithophile (‘rock-loving’), siderophile (‘iron-loving’), chalcophile ‘(ore-loving’ or ‘chalcogen-loving’), and atmophile (‘gas-loving’). Some elements have affinities to more than one phase. The lithophile group (shaded orange) is the largest and consists mainly of the highly reactive metals of the s- and f-blocks of the periodic table, a few non-metals, and the more reactive metals of the d-block. Most lithophile elements form stable ions with the electron configuration of a noble gas. The rest, including silicon, phosphorus and boron, form strong covalent bonds with oxygen. Their affinity for oxygen causes the lithophile elements to associate very readily with silica, forming relatively low density minerals that are found in the crust. The more soluble minerals formed by the alkali metals tend to concentrate in seawater or in very arid regions where they can crystallise. The lithophile group includes lithium, sodium and potassium; beryllium, magnesium and calcium; titanium, chromium, tantalum and tungsten; aluminium, silica, phosphorus, and chlorine; thorium, uranium, and the lanthanide series. Several transition metals, including chromium, molybdenum, iron and manganese, show both lithophile and siderophile characteristics. Although they form strong bonds with oxygen and are never found in the crust in the free state, metallic forms are thought to exist in the core. The siderophile elements (pink) are the high-density transition metals which tend to sink into the core because they dissolve readily in iron, either in solid solutions or in the molten state. The siderophile elements include gold, cobalt, iron, manganese, molybdenum, nickel, and the platinum group elements. Many of them have no affinity for oxygen and form stronger bonds with carbon or sulphur. They are bound through metallic bonding with iron in the core. Chalcophile elements (yellow) are metals or the heavier non-metals that have a low affinity for oxygen and prefer to bond with sulphur and/or a chalcogen other than oxygen to form highly insoluble sulphides. They include copper, zinc, arsenic, silver, tin, mercury and lead. Chalcophile elements do not sink to the core but because these sulphides are denser than the silicate minerals they are found at a lower level than the lithophile elements. The atmophile elements (blue) are hydrogen, carbon, nitrogen and the noble gases, e.g. helium and argon. Also called ‘volatile elements’, they occur in liquids and/or gases at temperatures and pressures found on the Earth’s surface. Hydrogen is also classed as an atmophile: water is classified as a volatile because most of it is liquid or gas, even though it does exist as a solid. Goldschmidts tolerance factor The tolerance factor is an indicator for the stability and distortion of crystal structures. It was originally developed by Goldschmidt in 1926 and used to describe the perovskite structure. The tolerance factor can also be used to calculate the compatibility of an ion with a crystal structure. The Goldschmidt tolerance factor (t) is a dimensionless number that is calculated from the ratio of the ionic radii (image 2). In the perovskite structure, where the tolerance factor is 0.9–1, the a and b ions are of an ideal size, as in strontium titanate and barium titanate, which both have cubic symmetry. Where the tolerance factor is 0.71–0.9 the a ions are smaller than ideal, as is the case with the Ca2+ ions in perovskite itself, and the crystal is slightly distorted, resulting in the symmetry being reduced to orthorhombic (image 3). Tolerance factors are now also used for ilmenite. Goldschmidt also took great interest in the practical applications of science; the utilisation of olivine for as an industrial refractory can be traced back to him, and he was for many years head of the Norwegian Committee for Raw Materials. In 1929 Goldschmidt became Professor of Mineralogy in Göttingen, Germany but returned to Oslo in 1935. In 1942 he, being a Jew, was arrested on the orders of the German occupying powers. As he was about to be removed to Auschwitz, he was told he could stay in Norway on the condition that he used his scientific expertise for the German authorities. He later fled to Sweden and then to Britain where he was assigned to the Macaulay Institute for Soil Research in Aberdeen. He attended scientific meetings around Britain and lectured at the British Coal Utilisation Research Association on the presence of rare elements in coal ash. He returned to Oslo in 1946 where died soon after. A further major work, ‘Geochemistry’, was edited and published posthumously in England in 1954. The Goldschmidt Conference, a major international conference on geochemistry is named after him. 1 The Goldschmidt Classification (Wikimedia Commons) 2 Equation for the Goldschmidt Tolerance Factor (t) 3 The Goldschmidt Tolerance Factor for the perovskite group and ilmenite (Wikimedia Commons) 4 Perovskite from the Susa Valley, Torino, Italy (photo: Leon Hupperichs, Creative Commons) 5 Victor Goldschmidt as a young man (Wikimedia Commons)
Posted on: Wed, 10 Sep 2014 12:50:01 +0000
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