A Petrographic and Micro-Analytical Framework for the Study and Classification of Meteorites

This contribution presents a petrographic, microstructural, and micro-analytical approach developed for the comprehensive study of ordinary chondrites, as part of a master’s thesis aimed at defining an analytical protocol for the petrological and minerochemical characterization of extraterrestrial materials. The ultimate goal is the establishment of a dedicated laboratory for the petrological study of meteorites, exploiting available instrumentation and acquired micro-analytical expertise to achieve both a complete classification of chondrites and a deeper understanding of the processes governing their genesis and evolution.

The study was carried out in collaboration with the Italian Museum of Planetary Sciences, where an internship allowed the examination of a reference collection of classified meteorite thin sections commonly used for educational purposes. Subsequently, three ordinary unclassified chondrites, provided by the “Museo del Cielo e della Terra” (San Giovanni in Persiceto, Bologna, Italy) and by a private collection, were investigated.

The analytical workflow includes: (i) macroscopic measurements and photographic documentation; (ii) petrographic analysis by transmitted and reflected light optical microscopy for microstructural and mineralogical characterization; (iii) SEM-EDS X-ray compositional mapping on the whole petrographic thin section as well as on selected chondrules and microstructural sites; (iv) SEM-EDS quantitative microanalyses of mineral phases; and (v) micro-Raman spectroscopy.

Preliminary results indicate that, from a chemical perspective, two of the unclassified samples can be assigned to the H group and one to the L group of ordinary chondrites. Petrographic observations classify the investigated meteorites as petrologic types 4 to 6. The most common chondrule textures observed include porphyritic and barred olivine, porphyritic olivine–pyroxene, granular olivine–pyroxene, radial pyroxene, and complex chondrules.

SEM-EDS compositional maps of entire thin sections and selected microstructural domains enable visualization of textural relationships, estimation of modal mineral abundances relative to metallic phases, and the development of a comparative framework among ordinary chondrites. Mineral chemistry data are compared with literature values to refine classification criteria. Micro-Raman spectroscopy is performed on opaque phases or on selected minerals for the correct identification of the polymorphic phase which constrains proper ranges of P-T conditions. Moreover, micro-Raman analyses are employed to characterize solid and fluid/melt inclusions within primary minerals, assess surface alteration features, and investigate dust extracted from fractures, providing insights into secondary processes related to atmospheric entry and post-impact evolution.