Scanning electron microscope images of Etna subsamples (#1, #2, #3, and #4) and JSC-1A Lunar regolith simulant subsamples (#8, #9, #10, #11, #12, and #13), with sizes of about a few to 500 μm. Different scales are used to show as best possible both the grain size distribution and the high intrinsic porosity of individual grains. The white line in the bottom right corner of each image provides the scale, equal to 100 μm (#8), 300 μm (#1, #2, #9, and #10), and 1 mm (#3, #4, #11, #12, and #13).