Gold Dust

Both things you can make from this apply Midas, which makes whatever you kill cough up extra coins. It is a farming tool, not a combat one. On a single boss kill the extra silver is noise. Across an hour of an event or a spawn farm it turns into real money.

Melee takes it as Flask of Gold, which means giving up the flask slot that would otherwise carry an imbue that actually raises your damage. Guns take it as Golden Bullets, a much easier trade when you are grinding rather than pushing progression. Buy a large stack of dust from the Merchant before you start a session, since walking back mid farm wastes more time than the dust costs.