Goldschmidt’s geochemical classification of the elements: The evolution of a nuanced hypothesis

Abstract Victor Goldschmidt’s research on the geochemical classification and distribution of the elements provided a foundation to understand what he called the “geochemical evolution” of the elements. Students of geochemistry often first learn a simplified version of the geochemical classification with four categories—siderophile, chalcophile, lithophile, or atmophile—based on affinities for a metal, sulfide, silicate/oxide, or gaseous phase, respectively. However, Goldschmidt’s evolving presentations of this concept were far more nuanced, with several iterations between the early 1920s and late 1930s. In his pioneering 1923 treatment, Goldschmidt focused on the distribution of the elements among metallic, sulfide, and silicate phases during Earth’s initial differentiation into a metallic core, sulfide-oxide layer, mantle, and crust. He drew evidence from the distribution of the elements in different meteorite phases, as well as metallurgical partition coefficients among coexisting metal, sulfide, and silicate slag–observations that informed his division of elements into siderophile, chalcophile, and lithophile elements. Goldschmidt linked his classification to crystal chemical controls, which ultimately stem from properties of electron shell structures of the elements. He also emphasized that his classification scheme is subject to the boundary conditions given by thermodynamic variables such as temperature, pressure, and redox conditions. Goldschmidt expanded on a second evolutionary cycle for magmatic differentiation with extensive analytical studies of crustal lithologies, including igneous, sedimentary, and biologically mediated deposits, and by 1929 his classification evolved to include a fifth group for the “biophile elements.” His environment-dependent geochemical classification of the elements became part of his principles and geochemical laws that provide the foundation to understand how the abundances and the distribution of the elements were established both for Earth’s surface environment and for the planet as a whole. Goldschmidt’s articulation of Earth’s “geochemical evolution” is a framing that incorporated a prescient description of the co-evolving geosphere and biosphere, thus anticipating the principles of “mineral evolution” by more than half a century.