"We followed the map as best we could, periodically checking our bearings using the chronograph and the sextants that the seer had given us. Eventually we found the deserted location that corresponded to the coordinates on the rapidly disintegrating map. And we began digging...
"We started a trench that went down about fifteen feet into the baking sand and headed due South. After a few hours our spades rang with the sound of steel on stone and as it did so the group gathered round to see what we had hit. Some hand digging revealed a dark black stone that had been carved with a strange texture on it's surface like a series of overlapping layers of petrified tendrils frozen for perhaps a thousand years. It looked and felt utterly alien, and yet our goal lay in the centre of this forbidding artefact.
Mining in a certain area turns all exposed skin (maybe just parts that are actively disturbing the chemicals that cause the reaction) of the those doing the mining to a dark blue color. Will wear off taking as many years/days spent in the mine. ... meeting a party of blue-skinned humans armed with pick-axes etc. Strange disease? Demon offspring? Curse? If they meet only one ex-worker, they will very carefully listen to any stories he says, no matter if drunken or insane, or just makes up to get a beer.