Iron meteorites consist overwhelmingly of nickel-iron alloys. General Name, Symbol, Number nickel, Ni, 28 Chemical series transition metals Group, Period, Block 10, 4, d Appearance lustrous, metallic Atomic mass 58. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ... An alloy is a combination, either in solution or compound, of two or more elements, which has a combination of at least one metal, and where the resultant material has metallic properties. ...

Occurrence

While they are fairly rare compared to the stony meteorites, comprising about 5.7% of witnessed falls, they have historically been heavily over-represented in meteorite collections. This is due to several factors: A meteorite is a small extraterrestrial body that impacts the Earths surface. ...

• They are easily recognized as unusual even by laymen, 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.

In fact, Iron meteorites account for almost 90% of the mass of all known meteorites, about 500 tons. All the largest known meteorites are of this type ^[1], including the largest -- the Hoba meteorite. Ablation is defined as the removal of material from the surface of an object by vaporization, chipping, or other erosive processes. ...

Origin

The majority of iron meteorites originate from M-type asteroids, which are fragments of the cores of larger ancient asteroids that have been shattered by impacts. The IIE chemical class may be a notable exception, in that they probably originate from the crust of S-type asteroid 6 Hebe. M-type asteroids are metallic asteroids; they are moderately bright (albedo . ... An asteroid is a small, solid object in our Solar System, orbiting the Sun. ... Approximately 17% of all known asteroids are of an S-type (for stony) composition. ... 6 Hebe (hee-bee, Greek ‘Ήβη) is a very large Main belt asteroid. ...

Composition

The overwhelming bulk of these meteorites consists of the alloys kamacite and taenite. Minor minerals, when occurring, often form rounded nodules of triolite or graphite, surrounded by schreibersite and cohenite. Kamacite is a mineral. ... Taenite is a mineral found naturally on Earth mostly in iron meteorites. ... Graphite (named by Abraham Gottlob Werner in 1789, from the Greek γραφειν: to draw/write, for its use in pencils) is one of the allotropes of carbon. ... Schreibersite is a rare iron nickel phosphide mineral, (Fe,Ni)3P, found in iron-nickel meteorites. ... Cementite or iron carbide is a chemical compound with the formula Fe3C, and an orthorhombic crystal structure. ...

Classification

Two classifications are in use.

The older Structural classification is based on the relative abundance of nickel to iron, which can be assessed from the appearance of polished cross-sections that have been etched with acid. ^[2] The categories are: General Name, Symbol, Number nickel, Ni, 28 Chemical series transition metals Group, Period, Block 10, 4, d Appearance lustrous, metallic Atomic mass 58. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ...

• Hexahedrites (low nickel)
• Octahedrites (average to high nickel), most common
• Ataxites (very high nickel), rare

The Octahedrites can be further divided up on the basis of the properties of their Widmanstätten patterns. Hexahedrites are a class of nickel iron meteorites. ... Octahedrites are a class of nickel iron meteorites. ... Octahedrites are a class of nickel iron meteorites. ...

A newer Chemical classification based on the proportions of trace elements separates the iron meteorites into classes corresponding to distinct asteroid parent bodies ^[3]: An asteroid is a small, solid object in our Solar System, orbiting the Sun. ...

• IAB classs
• IC classs
• IIAB classs
• IIC classs
• IID classs
• IIE classs
• IIG classs
• IIF classs
• IIIAB classs
• IIICD classs
• IIIE classs
• IIIF classs
• IVA classs
• IVB classs
• Ungrouped meteorites. This is actually quite a large collection (about 15% of the total) of over 100 meteorites which do not fit into any of the larger classes above, and come from about 50 distinct parent bodies.

References

1. The largest meteorites
2. structural classification
3. chemical classification
4. www.meteorite.fr

Links

http://www.chrisploof.com/ meteorite and precious metal rings and jewelry