Ataxite
A nickel-rich iron meteorite that shows no visible structure when etched.
The name ataxite means "without structure", and it describes how these iron meteorites look after etching. Most contain more than about 16 per cent nickel. At such high nickel levels, the kamacite plates that build a Widmanstätten pattern are microscopic, so an etched surface looks plain and uniform to the naked eye, though a microscope reveals a fine intergrowth of kamacite and taenite.
Not all ataxites are nickel-rich. A few are low-nickel irons whose original structure was erased by reheating, either in space or by people heating the metal after a find. The world's largest known meteorite, Hoba in Namibia, is a nickel-rich ataxite of about 60 tonnes, found in 1920 and still lying where it was discovered. Hoba belongs to the IVB chemical group, as do several other ataxites.
Ataxites can be recognised only after cutting and etching: the surface stays smooth and silvery, sometimes with faint sheen, rather than showing bands. They are heavy, strongly magnetic and often resist rusting better than low-nickel irons. If you ever see an iron meteorite displayed outdoors, as Hoba is, look but never chip it; damaging protected specimens is illegal in many places.
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