Octahedrite
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Octahedrites are the most common class of iron meteorites. They are composed primarily of the nickel-iron alloys: taenite - high nickel content, and kamacite - low nickel content.
Due to a long cooling time in the interior of the parent asteroids, these alloys have crystallized into intermixed millimeter-sized bands (from about 0.2 mm to 5 cm). When polished and acid etched the classic Widmanstätten patterns of intersecting lines of lamellar kamacite, are visible.
In gaps between the kamacite and taenite lamellae, a fine-granied mixture called plessite is often found. An iron nickel phosphide, schreibersite, is present in some nickel-iron meteorites as well as an iron nickel cobalt carbide, cohenite.
[edit] Chemical classification
Concentrations of trace elements are used to separate the iron meteorites into chemical classes, which correspond to separate asteroid parent bodies:
- IAB iron meteorites
- IC iron meteorites
- IIAB iron meteorites (includes also some hexahedrites)
- IIC iron meteorites
- IID iron meteorites
- IIE iron meteorites
- IIG iron meteorites (includes also some hexahedrites)
- IIF iron meteorites (includes also some ataxites)
- IIIAB iron meteorites
- IIICD iron meteorites
- IIIE iron meteorites
- IIIF iron meteorites
- IVA iron meteorites
For a full list see iron meteorites
[edit] Mineral
Octahedrite is also an obsolete synonym for anatase, one of the three known titanium dioxide minerals.
[edit] References
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