Notice that the smoothness of the booming sand grains appear to be somewhere between the Luddington beach sample (squeaking sand) and the Sand Mountain sample (booming sand) shown in Fig. 2 of the Contemporary Physics article (see Fig. 2 above in this web page).
micrograph 6 (bottom left has a 50 micron text-bar. Typical grain size is around 200--300 microns).
