Very rare in igneous and sedimentary rocks. Forms the majority of the earth's core.
Nickel is commonly reported in iron in quantities up to several percents; meteoric iron generally contains at least 5%, and up to 25% to 65%, nickel. Because of the instability of iron under oxidizing conditions and the abundance of oxygen in the Earth's crust and atmosphere, practically all terrestrial iron occurs in the divalent (ferrous) or trivalent (ferric) state combined with other metals and nonmetallic elements in silicates, oxides, sulfides, etc.
A solid-solution of carbon in alpha-iron, a deformed tetragonal phase in some meteorites and artificial steels. α2-Fe(Ni, Co) A solid solution of iron and up to one percent of carbon, the chief constituent of hardened carbon tool steels.