Hello, guys, Im new here. I'm wondering, what kind of sand should I use to reproduce this phenomenon: http://www.youtube.com/watch?v=X7LpmE9hl-c&feature=related I've tried several kinds of sand, but the phenomenon hasn't observed. What density should sand has? What is the fraction (diametr) of sand? Thank you. PS: I dont asking about origins of this effect. Just want to reproduce it.