I agree that it probably had no magical properties (three magic systems, and two almost dieties are enought I think), but that doesn't mean it isn't important. Why did Reen leave it behind that day? He took everything else he owned with him. This gets me thinking: Reen knew he was about to be caught. He knew the inquisitors were close to catching him, so early one morning, he takes all his things, and leaves, making Vin think he abandoned her. This was either to teach her a lesson, or so that she wouldn't go looking for him, or try to seek revenge or something like that. So Reen marches off, meets his death, swears Vin is dead, and dies. Vin thinks he is vanished and is long gone because he took all his things, gives up hope of ever finding him, and just contents herself to stay with Camon. But Reen left one thing behind. A piece of Obsidian with strange markings, for Vin. These strange markings are they simply a different language perhaps? What would happen if Vin showed the obsidian to Sazed I wonder. Does Vin ever mention some of the things she sees in other languages is framiliar?