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

Abstract

Mössbauer 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 Mössbauer spectroscopy in meteorites are proportional to the number of iron atoms in this mineralogical phase. This property of Mössbauer spectra can be the basis for constructing a method for the classification of ordinary chondrites. This idea was first explored at the Mössbauer Laboratory in Kanpur. This group suggested a qualitative method based on 2‐dimensional plots of Mössbauer spectral areas and thus classified properly some meteorites. We constructed a quantitative method using Mössbauer 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 Mössbauer 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.

Mӧssbauer spectroscopy as a useful method for distinguishing between real and false meteorites

“…We decided to verify this hypothesis using the 4M method. This method, published in Meteoritics & Planetary Science by Woźniak et al in 2019 [15], is able to determine the type of ordinary chondrite only on the basis of its Mössbauer spectrum. The 4M method works in two stages: at the beginning the socalled Mahalanobis distance is calculated, then, based on the knowledge of the Mahalanobis distance, the level of similarity of the tested meteorite to the particular type: H, L or LL is determined.…”

“…In the last 20 years several studies on the use of Mössbauer spectroscopy for classification of ordinary chondrites were published [2][3][4][5][6][7][8][9][10][11][12][13][14][15].…”

Application of Mössbauer spectroscopy for classification of ordinary chondrites – different database and different methods

“…In Warsaw group, we have been publishing papers on classification of ordinary chondrites since 2014 [12][13][14][15][16][17][18][19]. The database which we used for the creation of a new, fully quantitative method for classification of ordinary chondrites is composed of 59 Mössbauer spectra (22 type H, 20 type L and 17 type LL (Fig.…”

“…Hence, only the nonweathered or little weathered (paramagnetic doublet of Fe3+ smaller than 7%) ordinary chondrites' Mössbauer spectra are found in our database. All the results were shown in the supplementary Table 1 as published by Wozniak et al [19]. In this table, the percentages of spectral area associated with olivine (ol), pyroxene (pyr), metallic phase (met) and troilite (tr) were listed.…”

“…The database described above was used to formulate the method to determine the type (H, L or LL) of the investigated meteorite. We named it "4M method" and published it earlier this year (Wozniak et al [19]). The name of this method derives from four words starting with letter M: Meteorites, Mössbauer spectroscopy, Multidimensional discriminant analysis (MDA) and Mahalanobis distance.…”