Carbonaceous chondrites techniques

Other meteorite classes like C2, CO and ordinary chondrites contain much smaller inclusions less than 1 mm (MacPherson et al. 1988) and require ion microprobe techniques to evaluate the isotopic compositions. On the least metamorphosed side. Cl have very few inclusions or oxide grains, but are the carrier of the greatest amounts of stellar nanodiamond and other carbides (Anders and Zirmer 1993). As will be shown for Cr anomalies in carbonaceous chondrites, the survival of the mineral carriers of the anomalies also depends on the metamorphic grade of the meteorites. Nevertheless, isotopic anomalies have also been formd in higher metamorphic grade from other classes, especially in the reduced enstatite chondrites. 

Another analytical procedure for sample preparation including analyte separation and enrichment is the coprecipitation of the trace elements to be determined. The co-precipitation behaviour of Ti, Mo, Sn and Sb under two different fluoride forming conditions (at < 70 °C in an ultrasonic bath and at 245 °C using a Teflon bomb) has been studied to improve the accuracy of the trace analysis of these elements in Ca-Al-Mg fluorides, by ICP-MS.14 The applicability of this analytical method (including isotope dilution technique) was demonstrated for four carbonaceous chondrites and silicate reference materials of basalt or andesite.14... 

The study of chondrite matrices is both time-consuming and challenging, principally because of the fine-grained characteristics of the material. Transmission electron microscopy (TEM) has been the analytical technique of choice, because it provides textural and mineralogical information from the micron down to the nanoscale. Here, we briefly overview the main textural and mineralogical characteristics of matrices in very un-equilibrated chondrites, focusing principally on the carbonaceous chondrites. 

The analysis of the insoluble organic component (lOM) in carbonaceous chondrites is based on the techniques developed for coal, oil shales and petroleum source rocks. In order to analytically access the organic material the mineral phase of the meteorite is dissolved using a mixture of HCl and HF (9), leaving behind an organic residue that can be either processed further or used directly for analysis. 

A battery of complementary techniques is often necessary (and always desirable) to provide reliable, applications-oriented characterization of the bulk properties of (catalytic) carbon materials. Arguably the most useful ones are transmission electron microscopy (TEM), thermoelectric power (TEP) measurements, electron spin resonance (ESR) spectroscopy coupled with a superconducting quantum interference device (SQUID), and Raman spectroscopy. For example, among the recently reported virtues of Raman spectroscopy is the identification of graphite whiskers [152,153] in three carbonaceous chondrite meteorites (M. Fries and A. Steele, Science Online, Feb. 28, 2008), which contain some of the oldest matter in the solar system and has thus generated tremendous interest among astrophysicists. 

Pyrolysis products from carbonaceous chondrites are often interpreted as fragments from the kerogenlike aromatic-dominated macromolecular material. However, this interpretation is an oversimplification, especially when there is no efficient hydrogen donor as used in other pyrolysis techniques such as hydrous or HyPy (Figure 18.3). Free radical processes dominate during pyrolysis with cleavage of C-C bonds between the a and P carbons of side chains [36,37]. Benzenes... 

Since the 1950s, when the elemental abundance distribution depicted in Figure 1 became available, significant improvements have occurred in the accuracy with which the Solar System abundances are known. In part this is owing to the realization that Type I carbonaceous chondrites - made up of low-temperature condensates that escaped the many alteration processes which affected other classes of meteorites - closely approximate the condensable fraction of primordial Solar System material, and so represent our best opportunity of obtaining an abundance distribution which approximates reality. Isotope dilution mass spectrometry (IDMS) is an effective analytical method for determining trace element concentrations, because of the excellent sensitivity, accuracy and precision of the technique, and because a quantitative recovery of the element concerned is not required. The abundance of the... 

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