Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorite that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of two mineral phases: kamacite and taenite. Most iron meteorites originate from cores of planetesimals, with the exception of the IIE iron meteorite group The iron found in iron meteorites was one of the earliest sources of usable iron available to humans, due to the malleability and ductility of the meteoric iron, before the development of smelting that signaled the beginning of the Iron Age. Occurrence Although they are fairly rare compared to the stony meteorites, comprising only about 5.7% of witnessed falls, iron meteorites have historically been heavily over-represented in meteorite collections. This is due to several factors: They are easily recognized as unusual, as opposed to stony meteorites. Modern-day searches for meteorites in deserts and Antarctica yield a much more representative sample of meteorites overall. They are much more resistant to weathering. They are much more likely to survive atmospheric entry, and are more resistant to the resulting ablation. Hence, they are more likely to be found as large pieces. They can be found even when buried by use of surface metal detecting equipment, due to their metallic composition. Because they are also denser than stony meteorites, iron meteorites also account for almost 90% of the mass of all known meteorites, about 500 tons. All the largest known meteorites are of this type, including the largest—the Hoba meteorite. Origin Iron meteorites have been linked to M-type asteroids because both have similar spectral characteristics in the visible and near-infrared. Iron meteorites are thought to be the fragments of the cores of larger ancient asteroids that have been shattered by impacts. The heat released from the radioactive decay of the short-lived nuclides 26Al and 60Fe is considered as a plausible cause for the melting and differentiation of their parent bodies in the early Solar System. Melting produced from the heat of impacts is another cause of melting and differentiation. The IIE iron meteorites may be a notable exception, in that they probably originate from the crust of S-type asteroid 6 Hebe. Chemical and isotope analysis indicates that at least about 50 distinct parent bodies were involved. This implies that there were once at least this many large, differentiated, asteroids in the asteroid belt – many more than today. Composition The overwhelming bulk