Mössbauer Spectroscopy Applied to the Classification of Stone Meteorites

Abstract

The present classification of stone meteorites is essentially based on the distribution of iron in oxidated and reduced state (Prior plot). Evidently, a quantitative analysis of a larger number of mixed iron-containing mineral components encounters many difficulties. Quite recently, ⁵⁷Fe Mössbauer spectroscopy has been considered a valuable tool in this respect. One of the significant advantages of this method is that the individual components are analysed ‘in situ’ in a non-destructive way. Most important, a quantitative determination of Fe in olivine, pyroxene, serpentine, troilite, magnetite, hematite, Fe-oxyhydrates and other Fe(II)-Fe(III) minerals is feasible. An important factor is that the method can be applied successfully even to a minor component such as serpentine in carbonaceous chondrites - in contrast to normal mineralogical methods which here fail by reason of opacity.

About 60 stones, including 6 carbonaceous chondrites, were thus quantitatively analysed and classified by their Mössbauer characteristics in agreement with their conventional grouping. The resulting Prior plot of the falls gives evidence for the validity of the second Prior rule within each individual group. Weathering influences led to the formation of hydrated Fe(III) silicates and FeO(OH) which offer also a possibility for distinguishing between finds and falls. Identification of the products was possible by tempering experiments.