Fourth picture in the gallery shows what it looks like on the map/mini-map. It's an actual resource on the ground, like iron/copper/coal, and it isn't everywhere sand is anymore in the most recent versions.
I'm really, really enjoying the mod, congratulations!!!I'm going to try a new game just with your mod and slowly sizing with others and see what causes this problem of "disappearing" sand.
Hadn't tested it with Bob's mods, but after installing all of them sand still generates normally. In addition, looks like you can also make glass (the only use for sand) using Bob's method - quartz ore.