Determination of olivine fayalite–forsterite composition in ordinary chondrites by X‐ray diffraction

Abstract

Ordinary chondrites account for the majority of the described meteorites on Earth. To expand the toolbox of analytical techniques available to describe such specimens, this study evaluates the application of a previously described fayalite determination method by X‐ray diffraction (XRD) to equilibrated ordinary chondrites. A suite of ordinary chondrites, ranging from petrologic type 4 to 6, and types H, L, and LL were analyzed by both XRD and electron probe microanalysis. A comparison of the results shows good agreement between the two methods with an R2 of 0.95 and better agreement for homogenous ordinary chondrites above petrographic grade 4. The differences between the two methods can largely be attributed to analytical uncertainty, as well as differences between point and bulk sampling techniques. These differences were used to identify two polymict breccia samples, Peace River and Northwest Africa 10946. Of note is the effect of exposure of the ordinary chondrites to room temperature and humidity conditions after sample preparation (powdering) and the impact on measured fayalite content by XRD. As such, it is recommended that XRD analyses of meteorites be performed immediately after sample preparation.

The “Meteorite meter”: A handheld instrument for the combined measurement of magnetic susceptibility and electrical conductivity, with application to meteorite identification and classification

“…Oil immersion, that has been widely used for the classification of equilibrated ordinary chondrites (EOC) collected in the framework of the ANSMET program (Lunning et al., 2012), is now being abandoned as it resulted in relatively frequent misclassification due to the uncertainty on the estimate of silicate composition. X‐ray diffraction allows the classification of EOC, but remains relatively time‐consuming and has significant uncertainty (Di Cecco et al., 2022). Handheld XRF has been shown to distinguish successfully the three ordinary chondrite groups based on their bulk Fe/Mn ratio and is another powerful tool to distinguish some achondrite groups (Zurfluh et al., 2011).…”