Wiktionary:

> Plutarch tells us in Lysander 17 that, in early times, nails (ὀβελοί (obeloí)) were used as money, six of which made a handful (δραχμή (drakhmḗ)), and that the name was changed to ὀβολός (obolós).

In the (legendary) Spartan version of this, though, the currency was more cumbersome and deliberately less practically useful. You don't want people coveting money for its intrinsic utility — it's bad enough they'll covet it for its trade value! So the Spartan iron money was (allegedly) quenched in vinegar to ruin its intrinsic value.

https://en.wikipedia.org/wiki/Pelanor

It's unlikely that the legend corresponds to any ancient reality, though.