Strange Black Dust In Under-Sink Cabinet

[brainiac]

For the past few weeks I've noticed a very fine black dust/powder along one side on the bottom shelf of the cabinet under my kitchen sink. It's definitely not mould or anything similar, and looks like gunpowder or the black residue you'd find at the bottom of a tea caddy. It's not falling from the sink above (there's no shelf in the middle) and there's no sign of anything else unusual. No sooner have I wiped it away, than it's back in a couple of days. Any ideas gratefully received - it's driving me mad!

[Sam1960]

could be coming from the door hinges.
http://ths.gardenweb.com/discussions/2284576/help-black-dust-coming-from-door-hinges

[Davemano]

Is there a drawer above it

[brainiac]

Hadn't thought it could be anything to do with the hinges, Sam, as it goes back almost to the back of the shelf, but I'll certainly have a really good look. No, Dave, no drawer above it.

Many thanks, both

[Sam1960]

I would put a little oil on the hinges and see what happens ....

[brainiac]

Roger that, Sam. Thank you

[Chipchopper]

I know you said its definitely not mould but to me, it sounds like just the kind of place where you would expect to find black mould. If this is the case, cider vinegar or baking soda can get rid of it.
Insect frass would be my second guess, check for bugs or small holes in woodwork. I sometimes find woodlice in cupboards that are not used much.

[cassa333]

I've just noticed this as well in my cupboard.

It was because the runner had broken and the draw was rubbing the edge and it was basically shaving it off.

[brainiac]

Thanks for the further suggestions. It's definitely not to do with the hinges, as the dust is to one side, but at the back corner of the bottom of the cupboard, under where the dishwasher joins the waste traps etc. No sign of any kind of insect activity, everything is bone dry, and there is no drawer above, so nothing to abrade anything.