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Iron-Meteorites


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Structural Classification

Iron meteorites mainly consist out of two different nickel-iron minerals, the "beam- iron" kamazite with a nickel content of up to 7,5% and the "band-iron" taenite with a nickel content of 27 - 65%. According to share and distribution of the one or other mineral, Iron meteorites form specific structures, and thus by the classic meteorites science they are subdivided into three different structural classes.

 

Octahedrites
 
Hexahedrites
 
Ataxites

 

 

 

 

 

Octahedrites

Octahedrites consist of a more or less fine synthetic growth of kamazite and taenite that has the structure of the octahedar. If such a meteorite is polished and its surface gets corroded with nitric acid, this synthetic growth becomes visible in form of the so called Widmanstätten patterns, fascinating plays of geometrically arranged volumes and beams. Corresponding to the width of the kamazite bands, one distinguishes between these lower groups: the nickel scarce, broad Octahedrites with a bandwidth of over 1,3mm, the middle Octahedrites with a bandwidth from 0,5mm to 1,3mm as well as the fine, more nickel rich Octahedrites with a bandwidth of less than 0,5mm. Often further groups are distinguished to describe still broader or finer structures.

 

 

 

Hexahedrites

Hexahedrites consist almost exclusively of the nickel scarce kamazite and show no Widmanstätten pattern if they are polished and corroded. Although in many Hexahedrites, after the corroding fine parallel lines become visible, the so-called Neuman lines, that represent structural shaping in the kamazite structure and are maybe the consequence of an impact event, the collision of the Hexahedrite-mother body with another asteroid or of the bounce of the meteorite on the Earth.

 

 

 

Ataxites

Also Ataxites show after the corroding no structures at all, but in contrast to the Hexahedrites, they consist almost totally of taenite and possess only microscopic small kamacite lamellas. Thus they count to the nickel richest meteorites in general (over 16% nickel content), but also to the rarest. Until now not one fall of an Ataxite was observed! Yet the world of the meteorites is a crazy world: the largest meteorite on this Earth, the Hoba-meteorite from Namibia, with a weight of more than 60 tons, belongs paradoxically to the rare class of the Ataxites.

Chemical Classification