The Tavern

...to make add additional risk to attempting to test ID a crystal ball? (not that the other two are particularly safe to begin with).

Maybe it has some use as a throwing weapon? It's bigger than a stone, and unlike a large rock, cannot shatter. :p Doesn't stack and can't be enchanted though.

I'm pretty sure it's just another legacy item like scrolls of blank paper. There is no reason for its existence, but no developer has felt the urge to actually go into the code and terminate it yet.

There are some ideas on the wiki for making them useful, but they're part of some miscellaneous items overhaul that isn't even on the schedule for the next two release cycles.

I was planning on removing them at some point soon if nobody else does, yeah.