Siderophile element
A siderophile element prefers to dissolve in iron metal, such as nickel, cobalt, iridium, platinum and gold.
Siderophile means 'iron-loving'. Siderophile elements concentrate in metallic iron rather than in silicate rock or sulfide. They include nickel, cobalt, gold, and the platinum group elements: platinum, palladium, iridium, osmium, rhodium and ruthenium.
When a young planet or asteroid melted and its metal sank to form a core, the siderophile elements went with it. That is why Earth's crust is so poor in platinum and iridium and why iron meteorites, samples of asteroid cores, are rich in them. It also explains the classification of iron meteorites into chemical groups using the siderophile elements nickel, gallium, germanium and iridium.
The small amounts of siderophile elements in Earth's mantle are thought by many scientists to have arrived after the core formed, delivered by late impacts, sometimes called the late veneer. Spikes of iridium and other siderophiles in sediments are a classic sign of material from a meteorite impact.
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