Application of Mossbauer spectroscopy, multidimensional discriminant analysis, and Mahalanobis distance for classification of equilibrated ordinary chondrites

Abstract

Mossbauer spectra of equilibrated ordinary chondrites consist of two doublets due to paramagnetic iron present in olivines and pyroxenes and two sextets due to magnetically ordered iron present in metallic phases and troilite. The spectral areas of the different mineralogical phases found by M€ossbauer spectroscopy in meteorites are proportional to the number of iron atoms in this mineralogical phase. This property of M€ossbauer spectra can be the basis for constructing a method for the classification of ordinary chondrites. This idea was first explored at the M€ossbauer Laboratory in Kanpur. This group suggested a qualitative method based on 2-dimensional plots of M€ossbauer spectral areas and thus classified properly some meteorites. We constructed a quantitative method using M€ossbauer spectral areas, multidimensional discriminant analysis, and Mahalanobis distance (4M method) to determine the probability of a meteorite to be of type H, L, or LL. Based on 59 M€ossbauer spectra, we calculated by the 4M method, Scluster, the level of similarity of the Goronyo meteorite to the clusters. On the plot of ferrosilite versus fayalite, the point representing Goronyo is located on the border between H and L areas. Calculated by the 4M method, the meteorite Goronyo is 32% similar to type H, 75% to type L, and 11% to type LL. Additional mineralogical analyses suggested that the Goronyo meteorite would be classified as type L, although it was originally reported as type H in the Meteoritical Bulletin Database.