Iron meteorites

Nickel is found as a constitutent in most meteorites and often serves as one of the criteria for distinguishing a meteorite from other minerals. Iron meteorites, or siderites, may contain iron alloyed with from 5 percent to nearly 20 percent nickel. Nickel is obtained commercially from pentlandite and pyrrhotite of the Sudbury region of Ontario, a district that produces about 30 percent of the world s supply of nicke. 

Eig. 5. The Widmanstatten pattern ia this poHshed and etched section of the Gibbeon iron meteorite is composed of iatergrown crystals of kamacite and taenite, NiFe phases that differ ia crystal stmcture and Ni content. Ni concentration gradients at crystal boundaries ia this 3-cm-wide sample can be used to estimate the initial cooling rates and corresponding size of the asteroid from which the meteorite was derived. 

Stony Irons. The stony iron meteorites are composed of substantial iron and siUcate components. The paHasites contain cm-sized ohvine crystals embedded ia a soHd FeNi metal matrix and have properties consistent with formation at the core mantle boundary of differentiated asteroids. The mesosiderites are composed of metal and siUcates that were fractured and remixed, presumably ia the near-surface regions of their parent bodies. 

Phosphorus is the eleventh element in order of abundance in crustal rocks of the earth and it occurs there to the extent of 1120 ppm (cf. H 1520 ppm, Mn 1060 ppm). All its known terrestrial minerals are orthophosphates though the reduced phosphide mineral schrieber-site (Fe,Ni)3P occurs in most iron meteorites. Some 200 crystalline phosphate minerals have been described, but by far the major amount of P occurs in a single mineral family, the apatites, and these are the only ones of industrial importance, the others being rare curiosities. Apatites (p. 523) have the idealized general formula 3Ca3(P04)2.CaX2, that is Caio(P04)6X2, and common members are fluorapatite Ca5(P04)3p, chloroapatite Ca5(P04)3Cl, and hydroxyapatite Ca5(P04)3(0H). In addition, there are vast deposits of amorphous phosphate rock, phosphorite, which approximates in composition to fluoroapatite. " These deposits are widely... 

D. L. Massart, L. Kaufman and K.H. Esbensen, Hierarchical non-hierarchical clustering strategy and application to classification of iron-meteorites according to their trace element patterns. Anal. Chem., 54 (1982) 911-917. 

Meteorites on Mars. Meridiani Planum is the first Iron meteorite discovered on the surface of another planet, at the landing site of the Mars Exploration rover Opportunity [359]. Its maximum dimension is 30 cm (Fig. 8.38). Meteorites on the surface of solar system bodies can provide natural experiments for monitoring weathering processes. On Mars, aqueous alteration processes and physical alteration by Aeolian abrasion, for example, may have shaped the surface of the meteorite, which therefore has been investigated intensively by the MER instruments. Observations at mid-infrared wavelengths with the Mini-TES... 

Besides this iron meteorite, there have been four other rocks identified to be probably of meteoritic origin. These centimeter-sized pebbles, named Barberton, Santa Catarina, Santorini and Kasos, show troilite and/or kamacite signatures in the corresponding Mossbauer spectra [359]. The range of Fe oxidation states suggests the presence of a fusion cmst. The four cobbles have a very similar chemical composition determined by the APXS, and therefore they may be fragments of the same impactor that created Victoria Crater [361]. 

Harrison Brown understood enough about the geochemistry of uranium and meteorites to realize that the lead in iron meteorites should be primordial, unchanged since the solar system formed. So he went looking for a student familiar enough with mass spectroscopy to analyze the isotopes in the lead in ancient iron meteorites and in modern rocks. He found Patterson. 

Pat, Brown said, after you figure out how to do the isotopic composition of these zircons, you will then know how to get the lead. .. (in an iron meteorite). You ll be famous, because you will have measured the age of the Earth. ... 

Chondrites Achondrites Stony iron meteorites Iron meteorites... 

The mineral schreibersite (FeNiXP is present in meteorites, and in particular in iron meteorites. Polyphosphate minerals have not been found on Earth, except for a few kilograms of a calcium diphosphate-containing mineral in New Jersey (Keefe and Miller, 1995). 

Pasek and Lauretta (University of Arizona, Tucson) point to a further important source of phosphate they studied the corrosion of phosphide minerals from iron meteorites under various conditions in aqueous solution, e.g., using NaHCCb as a buffer, or in solutions containing MgCh and CaCL, as well as in the presence of ethanol and acetic acid. 

In all the experiments, the main decomposition products were phosphonates, which are also stable in concentrated solutions of Mg and Ca chlorides. In some experiments, pyrophosphate, and in smaller amounts triphosphate, could also be detected. The authors thus assume that the primeval ocean contained phosphonates as a source of phosphorus for reactions leading to biochemically relevant molecules. Iron meteorites could have delivered sufficient reduced phosphorus (Fe3P) to the primeval Earth, so the question of prebiotic phosphorus chemistry should be looked at in more detail in the future (Pasek and Lauretta, 2005). 

Another source of information about the elements in outer space comes from meteorites. Meteorites are made of the same elements known on earth, but they have some differences. Iron meteorites are mainly iron mixed with a little nickel, often formed into one huge crystal. Iron does not crystallize the same way on earth. 

Primarily iron and nickel and similar in composition to M-type asteroids iron, 91% nickel, 8.5% cobalt, 0.6%. A recent find of an iron meteorite on the surface of Mars is shown on p. 7 of the colour plate section... 

Fluorapatite is the only significant phosphorus-containing mineral in the Earth s crust and schreibersite has been found in iron meteorites. The only organic species to be found containing phosphorus in meteorites are the alkyl phosphonic acids. These are at least promising even if they do not contain the P-O-P phosphoester bond unit. 

We were quite elated, and it appeared that it was a rich field. Now, fifty years later, I must say that it wasn t as rich as we thought. But we have over the years discovered half a dozen natural radioactive elements, and two of these, the samarium-147 with its decay to neodymium-143 and rhenium-187 with its decay to osmium-187, prove to be of use in Nuclear Dating. The importance of rhenium is that it is iron soluble while the other radioactivities are insoluble in metallic iron. In fact, the best half life we have for rhenium-187 was obtained by measuring the osmium-187 to rhenium-187 ratio in iron meteorites which had been dated by other methods. This work was started many years ago by Dr. Herr and others in Germany. The half life is 43,000,000,000 years. 

There are also indications that Ru displays systematic deficits in Ru in iron meteorites and in Allende relative to terrestrial composition (Chen et al. 2003). A deficit in s-process isotopes of Ru is the favored interpretation. 

Chen JH, Wasserburg GJ (1983) The isotopic composition of silver and lead in two iron meteorites Cape York and Grant. Geochim Cosmochim Acta 47 1725-1737... 

Chen JH, Wasserburg GJ (1987) A search for evidence of extinct lead 205 in iron meteorites. Lunar Planet Sci 18 165-166... 

Chen JH, Wasserburg GJ (1990) The isotopic composition of Ag in meteorites and the presence of Td in protoplanets. Geochim Cosmochim Acta 54 1729-1743 Chen JH, Papanastassiou DA, Wasserburg GJ (2003) Endemic Ru isotopic anomalies in iron meteorites and in Allende. Lunar Planet Sci XXXIV 1789... 

Davis AM, Olsen EJ (1990) Phosphates in the El Sampal lllA iron meteorite have excess Cr and primordial lead. Lunar Planet Sci 21 258-259... 

The Se/ Se ratios of CDT and 3 other iron meteorite samples were determined by Rouxel et al. (2002). CDT had the greatest ratio, and the other meteorites ranged from -0.2%o to -0.6%o relative to CDT. Four basaltic reference materials, two glassy MORB s, and one peridotite also analyzed by Rouxel et al. (2002) were within 0.2%o of CDT. These results suggest that the earth s mantle is close in Se isotope composition to CDT, and that CDT is, tentatively, a reasonable proxy for the bulk composition of the earth. 

Beaudoin G, Taylor BE, Rumble III D, Thiemens M (1994) Variations in the sulfur isotope composition of troilite from the Canon Diablo iron meteorite. Geochim Cosmochim Acta 58 4253-4255 Birck JL, Allegre CJ (1988) Manganese-chromium isotope systematics and the development of the early solar system. Nature 331(6157) 579-584... 

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