Sand occurs naturally, http://www.nature.com/scitable/blog/saltwater-science/what_is_sand_made_of but it would totally be possible to make it. This is like fresh water. We are pumping the one already available because it's easier and therefore cheaper to exploit. But if we were to run out, there are ways to make our own. Initially raising the price until technology and infrastructures are amortized. Look at solar energy, initially much more expensive than coal and fossile energy, now reaching interesting lows.