![Illustration of the different size averages for Renazzo (after the data of Ebel et al. (2024)) on a back-scattered electron image of polished section 719sp3 of the Muséum national d’Histoire naturelle collection (Jacquet et al., 2012).-- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/10/Chondrule.png?fit=1200%2C677&ssl=1)
[astro-ph.EP] Chondrule sizes are an important discriminant of chondrite groups and chondrule formation theories. Yet most studies report 2D sizes without attempting the somewhat tedious corrections to 3D proposed in the past literature.
I show here that 3D size averages can be simply calculated directly from 2D averages of appropriate powers of sizes (and vice-versa), without having to reconstruct 3D distributions, although explicit formulas to that end are also provided. This illuminates the comparison between 3D and 2D arithmetic size averages, which are confirmed to be little different for the published datasets. Yet
I suggest another type of average, the “sphere-weighted average” (i.e. weighted by the chondrule equal-volume sphere area), a measure of the surface/volume ratio of the chondrule population, which is more robust against omission of small chondrules. While larger than the arithmetic averages, it is best in line with previous literature estimates based on less exhaustive surveys of chondrules.
Emmanuel Jacquet
Comments: Accepted to Meteoritics and Planetary Science
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2609.37178 [astro-ph.EP] (or arXiv:2609.37178v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2609.37178
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Submission history
From: Emmanuel Jacquet
[v1] Tue, 29 Sep 2026 10:03:02 UTC (2,441 KB)
https://arxiv.org/abs/2609.37178
Astrobiology, Astrochemistry,
