Iron is the most abundant element in the Earth’s crust and has four naturally-occurring stable isotopes. They are 54Fe, 56Fe, 57Fe and 58Fe. Despite its ubiquity, it is rarely found as a free metal, because it readily oxidizes, giving rise to reddish-to-brown oxides such as magnetite, hematite, goethite, limonite and siderite. These minerals are often mixed with carbon to produce the metal alloy known as steel, which is extremely strong.
The nuclear isotopes of iron have long been of interest to scientists. Unlike the lighter atoms of other metals, such as aluminium and magnesium, iron’s nuclei are extremely tightly bound. As such, it is very difficult to perform fission or fusion on these nuclei to liberate energy. This is why fission and fusion are normally carried out inside extremely massive stars, where the heavy nuclei can be produced more easily.
The isotopic composition of iron has also been of interest to astronomers and meteorologists. In particular, the correlation between the concentration of 60Ni, the daughter product of 56Fe, and the relative abundances of the stable isotopes of iron in the meteorites Semarkona and Chervony Kut suggests that 60Fe was present at the time of the remelting and differentiation of the asteroids that formed the solar system 4.6 billion years ago. This, in turn, would support the theory that fission of a heavier nucleus, such as 62Ni or 60Fe, played a role in the formation of the solar system. The isotopic composition of water can be used to determine the amount of iron reduction resulting from the decomposition of organic matter, since microbially-reduced iron has a different isotopic composition than unmodified water.