Unbreakable.

[Eye_Gore]

Well doesn't the title of the stone and the description of it kinda contradict itself? First it implies that it is "unbreakable". However the description clearly says "if you break it, you buy it". So then one could deduct that if it is unbreakable, how would I break it that I would be forced to buy it? Don't think too hard about that, a paradox may ensue, but wait the item is in itself a paradox. I think if it breaks a black hole will open up sucking everything into it, but by the event horizon, nothing would matter and I wouldn't have to buy it after all.

[DarkStar]

It's a marketing gimmick. They claim it's unbreakable to make you want to buy it, even though it's QUITE breakable, as evidenced by it being Desynthable.