Meteoritic iron

Iron does not occur in nature as a native metal. Lumps of meteoritic iron, which fell to the surface of the earth from outer space, are often found, however. It has been argued whether the earliest iron used by humans was of meteoritic origin or smelted from ores (Piaskowsky 1988). Combined with other elements, iron occurs in a varied range of ferruginous (iron-containing) ores that are widely dispersed on the upper crust of the earth some common iron ores often used for smelting are listed in Table 37. 

Chondrites Achondrites Stony iron meteorites Iron meteorites... 

Fischer-Tropsch synthesis over meteoritic iron, iron-ore and nickel-iron alloy. Geochim. Cosmochim. Acta, 40, 915-24. 

Equation (8.47), with t = 0 and the composition of lead from meteoritic troilite used for the initial isotopic ratio of lead, was used by Clair Patterson (1955,1956) to determine the age of the Earth. In the 1950s, the largest uncertainty in determining the age of the Earth was the composition of primordial lead. In 1953, Patterson solved this problem by using state-of-the-art analytical techniques to measure the composition of lead from troilite (FeS) in iron meteorites. Troilite has an extremely low U/Pb ratio because uranium was separated from the lead in troilite at near the time of solar-system formation. Patterson (1955) then measured the composition of lead from stony meteorites. In 1956, he demonstrated that the data from stony meteorites, iron meteorites, and terrestrial oceanic sediments all fell on the same isochron (Fig. 8.20). He interpreted the isochron age (4.55+0.07 Ga) as the age of the Earth and of the meteorites. The value for the age of the Earth has remained essentially unchanged since Patterson s determination, although the age of the solar system has been pushed back by —20 Myr. 

Murer, Ch. A., Baur, H., Signer, P., Wider, R. (1997) Helium, neon, and argon abundances in the solar wind In vacuo etching of meteoritic iron-nickel. Geochim. Cosmochim. Acta, 61, 1303-14. 

Cosmogenic radioactivity 53Mn is created continuously as anuclear collision fragment in meteorites when cosmic rays strike the meteoritic iron nuclei during the meteorite s journey to the Earth. This radioactivity is counted in the lab, alive today in the meteorite, and gives information on the transit time of the meteorite from parent body to Earth. 

There are two basic types iron meteorites and stony meteorites. Iron meteorites are fairly easy to recognize because they are composed of more than 90% iron. They attract a magnet, and are very dense. Stony meteorites, or chondrites, can look like an ordinary rock. 

Prior to 4000 B.c. Cold, copper, and meteoritic iron used occasionally without melting. Hammered into shape. Copper first annealed about 4000 B.c. 

Figure 3, Sw vs. exposure age for various iron meteorites. Iron meteorites having the oldest exposure ages also have the lowest Sw values. The dashed line shows the maximum extent to which the 8w values of iron meteorites can be lowered by interaction with thermal neutrons produced during cosmic-ray exposure (23). The hatched area indicates the initial 8w of the solar system as determined from HfrW data for Allende CAIs. Tungsten isotope data for iron meteorites are from (5, 19, 20, 24) and exposure ages are from (25).

We have studied the synthesis of fatty acids by the closed Fischer-Tropsch process, using various carbonates as promoters and meteoritic iron as catalyst. The conditions used were D2/CO mole ratio = 1 1, temperature == 400°C, and time = 24-48 hr. Sodium, calcium, magnesium, potassium, and rubidium carbonates were tested as promoters but only potassium carbonate and rubidium carbonate produced fatty acids. These compounds are normal saturated fatty adds ranging from C5 to Cis, showing a unimodal Gaussian distribution without predominance of odd over even carbon-numbered aliphatic chains. The yields in general exceed the yields of aliphatic hydrocarbons obtained under the same conditions. The fatty acids may be derived from aldehydes and alcohols produced under the influence of the promoter and subsequently oxidized to the acids. 

Nonoxidized and oxidized-reduced Canyon Diablo meteoritic iron produced fatty acids when potassium carbonate was admixed (runs 4-97 and 4-109). The level of potassium carbonate (0.1 g vs. 0.3 g) in the catalyst (0.5 g) had no eflFect on the production of fatty acids (runs 4-109 and 5-24). Oxidized Canyon Diablo iron and potassium carbonate did not produce fatty acids (run 4-94), thus showing that promoter effects are catalyst dependent. 

The synthesis of fatty acids by a Fischer-Tropsch-type process as described in this chapter required the use of a catalyst (meteoritic iron) and a promoter. Potassium carbonate and rubidium carbonate were the only compounds evaluated which unambiguously facilitated the production of fatty acids. These catalytic combinations (meteoritic iron and potassium carbonate or rubidium carbonate) also produced substantial amounts of n-alkenes (in excess of n-alkanes) and aromatic hydrocarbons. A comprehensive study of the nonacidic oxygenated compounds produced in Fischer-Tropsch reactions (20,21) was not made. However, in the products analyzed (all promoted by potassium carbonate), long-chain alcohols and aldehydes were detected. 

Fatty acids in relatively high yields (usually in excess of the yields of aliphatic hydrocarbons) can be produced in a closed-system Fischer-Tropsch process using meteoritic iron as a catalyst, provided potassium carbonate or rubidium carbonate is used as a promoter. Aldehydes and alcohols or oxygenated intermediate complexes attached to the catalyst may be the source of the fatty acids. 

Meteoric iron is just what the name sounds like it s iron that comes from meteors. For early civilizations, meteoric iron was one of the few available sources of relatively pure iron (that is, prior to when the extraction of iron from ore was discovered). Meteors containing meteoric iron are composed of mostly nickel-iron alloys. Iron meteorites often have a distinct appearance, and they are typically much easier to recognize than other types of meteorites. For this reason, they are discovered more often than other types of meteorites. Iron meteorites actually account for all of the largest meteorites that have been discovered. 

It is interesting to have a look at the development of iron production methods. At first man used only meteoritic iron, which was very rare and therefore expensive. Then people learnt how to produce iron by intensively heating its ores with coal on windy sites. Iron thus obtained was spongy, of low grade, and with large inclusions of slag. An important step in iron production was made with the inven-... 

M7 Meteorite iron with Widmanstatten structure, found in Xiquipilco, the Toluca region in Mexico. 

There are numerous ways to classify meteorites [14,15]. Meteorites jinds, which cannot be directly linked to a specific observed fall, are much more common than falls. The distinction between stones (silicate meteorites), iron meteorites, and stony-irons is straightforward but ignores the significant genetic differences amongst stony meteorites. More recent nomenclature systems make a primary distinction between chondrites and non-chondrites, whereby the latter group includes all types of igneously differentiated meteorites (Table 10.1). 

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