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

1V. E. Di Cecco,1,2B. C. Hyde,1K. T. Tait,1R. I. Nicklin
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13824]
1Department of Natural History – Mineralogy, Royal Ontario Museum, Toronto, Ontario, M5S 2C6 Canada
2Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston, Ontario, K7L 2N8 Canada
Published by arrangement with John Wiley & Sons

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.

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