What is this thing? Is it dangerous? Is it useful?
I've scoured the Technic Pack Wiki and I'm stumped. I don't even know which of the pack's mods this thing comes from. The page on obelisks I did find appears to be an entirely different structure. This thing I'm looking at is not a Mystcraft obelisk – they aren't connected to the ground, and in any case I've found them in my overworld too. They're definitely from some other mod in the pack.
I haven't had the courage to mess with them yet (apart from walking around under it and learning that I don't immediately explode or turn into a zombie), but I've just found a Mystcraft world where there are a half-dozen right around the spawn – if I can exploit them somehow I've hit the motherlode.