siderophile element[′sid·ə·rə‚fīl ′el·ə·mənt]
any of a group of transition elements belonging for the most part to group VIII (3d-5d) of the periodic system of elements (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt) but also including certain neighboring elements (Mo, Re). Sometimes Au, P, As, C, Ge, Ga, Sn, Sb, and Cu are also classed as siderophile elements. Siderophile elements are located at the minima on the curve showing the dependence of the atomic volume of elements on the atomic number. The similar chemical and physical properties of the atoms, caused largely by the structure of outer electron subshells, suggests a common natural origin.
In the earth’s crust, siderophile elements occur either in the native state (native platinum, iridosmine group) or in lower-valence compounds. Siderophile elements exhibit a special chemical affinity for arsenic (arsenides of Pt, Co, Ni, Fe) and a slightly lesser one for sulfur (primarily Mo and Re, also Pd, inferior quantities of Fe, Co, Ru, Pt). With the exception of Fe, which is extremely widespread in the earth’s crust, and the much less abundant elements Ni and Co, the siderophile elements have very low clarkes. Platinum metals have a reduced capacity for geochemical migration.