Chondrule size averaging in two and three dimensions

Chondrule sizes are an important discriminant of chondrite groups and chondrule formation theories. Yet most studies report 2‐D sizes without attempting the somewhat tedious corrections to 3‐D proposed in the past literature. I show here that 3‐D size averages can be simply calculated directly from 2‐D averages of appropriate powers of sizes (and vice‐versa), without having to reconstruct 3‐D distributions, although explicit formulas to that end are also provided. This illuminates the comparison between 3‐D and 2‐D arithmetic size averages, which are confirmed to be little different for the published data sets. 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 whole 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.