I remember reading about an interesting event which happened in the early 19th century, in the Habsburg Empire.
A criminal organization, mainly composed of workers and corrupt administrators at a gold mine, minted prefect-quality gold coins illegally. Normally, the extracted gold had to be handed in, in exchange for a very low commission, so they handed in only part of the mined gold, minting the rest into coins illegally. However, instead of producing counterfeit coins with a lower than official gold content, they minted coins which had the same gold content as the real ones.
When the operation was busted, the confiscated coins were marked (by hammering a nail through them, if I remember correctly) and transported away to be destroyed, probably to be cast into bullion or to be minted.
This is what I don't understand, why was it necessary if the coins had the required gold content?
The criminal operation was definitely a loss for the government, but from the point of view of macroeconomics it shouldn't have influenced the supply of money. If the criminals wouldn't have minted it, I guess that probably the government would have. So, why were those "perfect" coins needed to be destroyed, if they were to be later re-minted anyway?