Non-chondritic meteorites

The systematic variations in oxygen isotopes provide an independent means of classifying chondrites that generates the same groups as the chemical compositions. The oxygen isotopes also work for classifying non-chondritic meteorites. Oxygen isotopic compositions are somewhat easier to obtain than detailed chemical data and so are often used to nail down a classification. 

Irons are non-chondritic meteorites that are predominantly metal. Iron meteorites formed by melting of, most likely, chondritic material and segregation of metal melt from silicate. Many apparently represent asteroidal cores, although some may have formed as dispersed metal pockets in the parent asteroids. 

The ureilites (Fig. 6.7c) constitute the second largest group of non-chondritic meteorites (Takeda, 1987). They are composed primarily of olivine and pyroxene, with interstitial... 

Mittlefehldt, D. W., McCoy, T. J., Goodrich, C. A. and Kracher, A. (1998) Non-chondritic meteorites from asteroidal bodies. In Planetary Materials, Reviews in Mineralogy 36, ed. Papike, J. J. Washington, D.C. Mineralogical Society of America, pp. 4-1 to... 

Mittlefehldt D. W., McCoy T. J., Goodrich C. A., andKracher A. (1998) Non-chondritic meteorites from asteroidal bodies. 

Messenger S, Walker RM (1997) Evidence for molecular cloud material in meteorites and interplanetary dust. In TJ Bematowicz, E Zinner (eds) Astrophysical Implications of the Laboratory Study of Presolar Materials. American Institute of Physics, Woodbury, CT, p 545-563 Mittlefehldt DW, McCoy TJ, Goodrich CA, Kraher A (1998) Non-chondritic meteorites from the asteroid belt. Rev Mineral 36 3.01-4.195... 

There are four main types of non-chondritic meteorites (Table 10.1). Primitive achondrites, such as the acapulcoites and lodranites, are thought to be from asteroids that experienced only incipient or limited melting (Table 10.1). In contrast, achondrites, iron meteorites, and stony-irons are considered to represent parent bodies that featured widespread melting processes, which ultimately led to planetary differentiation and the formation of a metallic core and a silicate-rich mantle and crust [14, 15]. 

Non-chondritic meteorites from asteroidal bodies, in Planetary Materials (ed. J.J. Papike), Mineralogical Society of America, Washington, DC,... 

Some of the chondritic meteorites contain grains (including crystalline and amorphous silicates, diamonds, silicon carbide, graphite, metal oxides, and metal nitrides) that have been identified as presolar based on non-solar isotopic ratios (Zinner 1988 Anders Zinner 1993 Bematowicz et al. 2006), particularly for... 

Paul R. L. and Lipschutz M. E. (1990) Consortium study of labile trace elements in some Antarctic carbonaceous chondrites Antarctic and non-Antarctic meteorite comparisons. Proc. NIPR Symp. Antarct. Meteorit. 3, 80-95. 

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). 

Essentially the same amino acids, and nearly equal quantities of D and L enantiomers, were detected in the Murray meteorite, another type II carbonaceous chondrite [6]. Recent expeditions to Antarctica have returned with a large number of meteorites, many of which are carbonaceous chondrites. These may have been protected from terrestrial contamination by the pristine Antarctic ice. Careful analysis of two of these, the Yamato (74662) and the Allan Hills (77306), both type II carbonaceous chondrites, by ion exchange chromatography, gas chromatography, and GC/MS, have detected a wide variety of both protein and non-protein amino acids in approximately equal D and L abundances [9,10]. Fifteen amino acids were detected in the Yamato meteorite and twenty in the Allan Hills, the most abundant being glycine and alanine. The amino acid content of the Yamato meteorite is comparable with that of the Murchison and Murray, but the Allan Hills contains 1/5 to 1/10 that quantity. Unlike earlier meteorites from other locations, the quantities of amino acids in the exterior and interior portions of the Yamato and Allan Hills meteorites are almost identical [9,10]. Thus, these samples may have been preserved without contamination since their fall in the blue ice of Antarctica, which js 250,000 years old in the region of collection. 

Non-volatile materials in asteroids included 1. presolar (interstellar) dust, and 2. dust condensed from a chondritic vapor in the inner solar system where presolar silicate and carbon dusts had evaporated at 2000 K during a thermal flare-up phase of the young Sun [71]. Evidence for both dust sources can be found in carbonaceous meteorites albeit they were modified by aqueous alteration below 400 K, or thermal alteration up to 800 K in their parent bodies [69,72,73]. When metastable carbynes were not obliterated by parent body alteration, these particular meteorites would be candidates for searches of carbynes formed (probably by condensation) around C-rich YSOs (interstellar dust), in the inner solar system, or both. 

In order to compare the atomic silicon-normalized Cl chondrite abundances in Table 2 (N(Si) = 106 atoms cosmochemical abundance scale) with the photospheric abundances on the hydrogen-normalized scale (A(H) = 12 astronomical abundance scale) in Table 3, the data must be converted to a common scale. One cannot easily convert the meteoritic data to the H-normalized astronomical abundance scale because H is depleted in meteorites. However, a comparison can be done for the non-volatile rock-forming elements. The difference of the logarithmic Si-normalized abundances of Cl chondrites to the abundances on the astronomical scale is more or less constant for many elements. This shows that the relative abundances in the photosphere and Cl chondrites are similar. 

Figure 6. Distribution of Xe and among the various components in the Orgueil Cl carbonaceous chondrite. Because in primitive meteorites virtually aU (non-solar) trapped gases are contained in acid-resistant phases (e.g., Ott et al. 1981), where a better separation of components is achieved during stepwise heating, the numbers shown are based on such residue data (Huss and Lewis 1995) for neon and xenon in the Q (PI) component on the HF/HCl residue data, for the Xe-P3 and Xe-HL components on the etched residue data. Shown are only components which contribute more than 1% to the total.

The concentrations of potentially mobile trace elements in H5 and L6 chondrites of Antarctic and non-Antarctic origin (falls only) reported by Lipschntz (1989) permit the conclusion with 90% or higher confidence that the trace-element concentrations of Antarctic meteorites actually do differ from those of the non-Antarctic falls. However, the cause for this difference is still in doubt. On the one hand, the Antarctic meteorites may have originated from a different set of... 

The apparent enrichment of Antarctic meteorites in iodine and, to a lesser extent, in chlorine is expressed in Table 18.7 by the Antarctic/non-Antarctic ratios of all four elements. The iodine ratios range from 25 in shergottites, to 46 in eucrites, and to 120 in howardites. Even Antarctic carbonaceous chondrites and ordinary chondrites (H) are enriched in iodine by factors of 24 and 2.5, respectively (not shown). These results demonstrate that the Antarctic meteorites are not pure and pristine as expected, but have been extensively contaminated by iodine and, to a lesser extent, by fluorine and chlorine. 

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