Crystal chemistry of scandium as a trace element in minerals

Publisher Website
Google Scholar
Abstract
A dominant theme in the geochemistry of scandium, originally suggested by G oldschmidt and P eters has been the supposed diadochy of the Sc 3 ion with the Fe 2 and Mg ions. Studies of the crystal chemistry of synthetic Sc compounds, especially with regard to the solid-solution relations of Sc as a major component in synthetic systems, now indicate that the distribution of Sc 3 as a trace element in the lithosphere is based on a diadochic relation to 6-coordinated (Fe 3 ,Al). This is supported by the isostructural relation between many oxycompounds of Sc 3 and of (Fe 3 ,Al), and by recent measurements of the Sc–O distances in numerous compounds. The radius of Sc 3 in 6-coordination with oxygen, although variable depending on the ionic-covalent proportions in the bond and other factors, is much smaller than the traditional value 0.83 Å of Z achariasen and averages about 0.73 Å or less. The close crystallochemical relation of Sc 3 to In 3 is not displayed in nature, but there are limited solid solutions with Y 3 , Er 3 –Yb 3 , Ti 4 , Sn 4 and Zr 4 in certain geochemical environments.