In Mongolia's gold rush economy, money has become such an emphatically localized and contentious object that its cash value cannot be presumed. Drawing on Mongolian notions of “polluted money,” I argue that, in this context, cash value is determined not only by a banknote's status as legal tender but also by local understandings of its materiality. Confronted with the intense pollution that attaches to gold miners’ money, shopkeepers change the face value of the money and effectively set higher prices in a region with increasing numbers of dependent customers. Rather than challenging or subverting money's national indexicality, this redenomination of state currency reflects people's critical position within a troubled economy of pollution. This case demonstrates that currency, like any other object, is a social medium that is intimately tied to the physical and cosmological world.