I believe Eloraam has future plans for marble as a calcium carbonate source. I think a more appropriate process here would be to dump sandstone into an extractor to yield calcite dust/cement, and then smelt (or compress?) that into marble. Adjusting the extraction result in the future to match Eloraam's plans (and Forge's ore dictionary), just to keep these two great mods in sync. I don't know how "realistic" that process is, but it seems to grok with my several-minute read through Wikipedia. It could be an alternate source of CF as well, since CF is kind of like a cement, right? It's a stretch, but then again, you start the game by punching down a tree.