They have a lot of rocks there. The sands are because of the weathering of the rocks. And they have a lot of sun. Which would make grounding of rocks feasible. That could allow them to use desert sand too. Or they might find a mix between traditional and desert sand.. and some special ingredients. who knows!

if you never try, you won't find it out.

It's a way of creative problem solving. If they build it. In the "middle of", suddenly, something is not enough, then you do have to find a solution.