I keep glancing at the artifact. I understand why the Iron Brotherhood's leader didn't want it. Since it has no apparent use, all it does is remind him of the tribesman who died seizing it from that giant spider.
Can it really be useless, though? They described the artifacts that activated the obelisk as looking similar to it, so I headed to the nearest obelisk to see if I could get a response. No luck. Maybe it activates something else?
Of course! The platform in the cave! It's a long shot, but it's the only thing I can think of that's similar to the obelisks. Definitely worth a try.