I would suggest obsidian, but perhaps the well known "fools' adamantine" would seem appropriate? It is, truth to be told, the most dwarfy material possible, and in most fortresses, it is one of the most common materials, which would make it less of a load on the fort's capacities.
OOC: If we're going for the more realistic route, we can't actually use lava/magma to get obsidian. It's about ten kilometres (6 miles or so) beneath the Earth's crust, and the Earth is in the low range of what sort of planets are human-habitable. Then again, no one knows how large a single Z-level is, so the magma sea could easily be that deep.
OOC
Well either you guys are really polite or for some reason no one had anything to post. Either way I am grateful for the break.
Of course obsidian is a bit of stretch, would be far too much effort for something like an arch.
Anyway, not proposing IC since I don't think Cain would do so at the current time but this is what I would, I shouldn't say but he would probaly support whatever is proposed, D4E's, Kerod's old "arch", Mine.
Fortifications cause, well they look nice imo, but maybe just walls. Silver because we have plenty to spare, wanted to use gold or iron, but iron hardly sounds pretty or fancy (and should be saved for making armor and weapons as we need them) and gold would be gaudy unless we used only a little.
"st" is for statues, thinking metal for the inside section statues, stone for the roof statues, but meh these are just personal thoughts. So wiki wise, still need the miners hall, still having trouble?
Can make it for you either in proper DF for the furniture, or just do the usual, preference?