You're very close to reality, Joggie! Not exeactly quartz, but some rock that resembles it. Found during my walks in the neighbourhood, where there are many nurseries meant to provide the elements for a Japanese garden...among which are also rocks. They are quite expensive, as one cannot find them by the side of the road.From what I saw in photos of glaciers.....it was a quite close resemblance. Thank you so much for taking the time to visit, always pleased by your comments! Regards, YT