Geode

The Geode deals 1 damage per swing — not a real weapon in a practical sense — but carries a 5% chance to shatter on any use and pay out 15-30 coins. That payout is substantial early in a run, and since the break chance is low, it functions as a normal weapon most of the time with an occasional windfall attached. It's part of the Rock and Gemstone item sets and is specifically obtained through the Arock event rather than standard loot pools.

The best use of a Geode is to take cleanup swings at near-dead enemies at the end of fights — you get to fish for the coin proc without risking losing your weapon mid-battle. Once it breaks, it's gone, so don't rely on it as a primary weapon. Keep something else ready in your kit before it shatters.