ATAXITE
Ataxites are rare iron meteorites that lack the Widmanstätten Structure seen in octahedrites and the Neumann Lines seen in hexahedrites. Ataxites are said to be internally structureless. Cut & polished & nitric acid-etched surfaces of ataxites show a finely crystalline texture that would be described as aphanitic if it were a terrestrial igneous rock.
Compositionally, ataxites can be relatively rich in the mineral taenite (nickel-rich Fe-Ni alloy, with 27-65 wt.% nickel), or they can be finely crystalline mixes of taenite and kamacite (iron-rich Fe-Ni alloy, with ~5.5 wt.% nickel).
Ataxite (field of view ~2.5 cm across) - a cut, polished, nitric acid-etched surface of the Santiago Papasquiero Meteorite, found in 1958 in Durango, Mexico. It consists of a finely crystalline mix of kamacite & taenite, plus other minor minerals. Santiago Papasquiero is a strange ataxite that appears to be a completely metamorphosed and recrystallized octahedrite. Most recrystallized octahedrites still retain vague hints of the original Widmanstätten structure. This meteorite doesn't have any, so it isn't an octahedrite - it's an ataxite.
Published chemical info. indicates that Santiago Papasquiero has 7.5% nickel content overall. The kamacite component has 6.8% Ni. The taenite component has 30% Ni.
(More info. on the Santiago Papasquiero Meteorite)
Ataxite - weathered individual of the taenite-rich Chinga Ataxite from the Tannu Ola Mountains, Siberia, Russia. The nickel content of this meteorite is 16.7%. An associated impact crater is not yet known for this meteorite. Chinga Meteorites have been exposed to Earth surface conditions for >2000 years.
(public display at meteorite museum at Odessa Impact Crater, Texas, USA)
(More info. on the Chinga Ataxite)
Some info. from:
Buchwald (1975) - Handbook of Iron Meteorites, Volume 3: 1080-1083.
Grokhovsky et al. (2000) - Mössbauer spectroscopy of the Chinga Meteorite. 63rd Annual Meteoritical Society Meeting Abstracts.