M 7.4. Beneath the Surface
Section Appendix
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Mean Grain Size of Lunar Regolith by Depth

Sample Depth Mean Grain Size <
~0 80
4 68
7 93
12 75
17 75
22 85
28 110
34 90
40 90
46 103
48 109
54 139
Average 93

Sizes are approximate, measured in microns.

Reference: the Lunar Sourcebook

The data is from the Apollo 15 site, about 20 m away from the rim of Hadley Rille, where the regolith is relatively thin and immature. The numbers themselves are from drive-tube core 15010/11, with simple locations and and mean grain sizes for individual samples. The core penetrates the upper 60 cm of a 1 m thick reolith.

This sample is closer then usual to the bedrock, and there is continuous mass wasting into the rille, so the median grain size is larger then samples collected elsewhere.

Features of this sample which appear to be consistent among other samples are the three peaks and troughs in particle size, although the depth at which these characteristics appear may vary by a decimetre either way (the features appear to be compressed in this sample). The lower depths appear to be unrepresentative, probably due to the close proximity of bedrocks.

M 7.4. Beneath the Surface

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