I know that Xaren are listed as eating magical weapons, shields, etc... but will regular Xorn eat nonmagical items, or just minerals and gems? The reason I ask is that I want to create a Xorn shopkeeper that sells various things (including metalic items like weapons) for jink, which the Xorn then eats! (I'm working on how it aquires stuff to sell if it doesn't use jink - maybe the Xorn is a thief! Or maybe it only eats part of its earnings, maybe the cheap jink like copper pieces...) Anyhow, the thing hinges on whether the Xorn would be inclined to eat the items it's offering for sale. (I supposed it could only stock nonmetalic items, but how many berks will line up to buy torches and clubs?)
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The SRD entry for xorns mentions that they eat metal, so sure enough, your Xorn could eat gold, silver, and maybe copper jink.
Does it necessarily have to be a shopkeeper? Perhaps it provides services as an assayer -- it can identify adulterations, alloys, gems, and the like by taste! It takes a cut of the proffered items, say 1%, to check for counterfeits and classify minerals and metals. It could easily serve as an importer of raw materials of higher quality than the Foundry works; it would carry precious metals and gems, buy them off of adventurers who wanted to offload them, and sell them to jewelers and Sigil's mint. It makes enough of a profit from the traffic that consuming a bit of its wares as food is supportable.
It could also exchange foreign coinage, since it doesn't have to spend the coins it takes on food; it just eats them.