Gold and silver had been used as a medium of exchange largely in long-distance trade; it was also stockpiled in (for instance) Mesopotamian temples as a store on value on which people could make credit arrangements, rather like the gold kept underneath the New York Fed at Liberty street nowadays, which can be moved back and forth between different vaults but never seems to leave the complex itself.

I was talking about the use of precious metals in small denominations for everyday purposes, which was definitely not going on in ancient Mesopotamia, let alone Egypt (the scales weren’t made accurate enough to measure such tiny pieces of silver as would have been required to buy eggs and shovels and the like) — here again people seem to have relied on credit. The first markets where people seem to have been using coins for everyday purchases might have been in Greece, though they soon followed in the Ganges valley, N. China, etc.
 

Relevant to our other convo, gold and silver (and cows and tobacco and wampum) were mediums of exchange long before coinage. Perhaps coinage was a slight convenience over grains of gold, but this is set against the ability to debase (inflate) the currency.