Random magical item.. I enjoy giving a mix of useful and not so useful items in my games.
Either this is the result of a failed alchemy attempt, or Thurs, the magic-using troll who enjoys rocks, created this machine.
A plain lead container about the size of a large jar that faintly hums with magic. On the inside of the lid are stick figures demonstrating steps to activate the item.
1. Put something in container.
2 . Put on lid.
3. Twist lid.
4. Open container.
If you put an item in it and twist the lid, that item becomes a rock. (Hopefully they don’t put something valuable in). If you have a rock in the container, the rock changes to a new rock. The container can hold about 10 rocks.
Pretty reliably 1/1000 a gem pops out.