The Isotope Geochemistry of Ni

Abstract

Nickel is an iron-peak element with 5 stable isotopes (see Table 1) which is both cosmochemically abundant and rich in the information carried in its isotopic signature. Significantly, 60Ni is the radiogenic daughter of 60Fe, a short-lived nuclide (t1/2 = 2.62 Ma; Rugel et al. 2009) of a major element. 60Fe has the potential to be both an important heat source and chronometer in the early solar system. 60Ni abundances serve to document the prior importance 60Fe and this is a topic of on-going debate (see Extinct 60 Fe and radiogenic 60 Ni ). The four other stable Ni nuclides span a sizeable relative mass range of ~10%, including the notably neutron-rich nuclide 64Ni. The relative abundances of these isotopes vary with diverse stellar formation environments and provide a valuable record of the nucleosynthetic heritage of Ni in the solar system (see Nucleosynthetic Ni isotopic variations ). Ni occurs widely as both elemental and divalent cationic species, substituting for Fe and Mg in common silicate structures and forming Fe/Ni metal alloys. The Ni isotope chemistry of all the major planetary reservoirs and fractionations between them can thus be characterized (see Mass-Dependent Ni isotopic Variability ). Ni is also a bio-essential element and its fractionation during low-temperature biogeochemical cycling is a topic that has attracted recent attention (see Mass-Dependent Ni isotopic Variability ). ### Notation Much of the work into Ni has been cosmochemical, focussing on the nucleosynthetic origins of different meteoritic components. Such studies have primarily investigated mass-independent isotopic variations, both radiogenic and non-radiogenic, which require choosing a reference isotope pair for normalization. Throughout this work we use 58Ni–61Ni as the normalizing pair, in keeping with current practice in the field. An alternative 58Ni–62Ni normalization scheme has previously been used for bulk …