Chisel

A Chisel is used to cut uncut gems into cut gems, and cutting gems into bolt tips. A Chisel can be purchased from Bob for 1 coin(s).

Money making with a Chisel
Buying uncut gems from Bob and cutting them into cut gems is quite a common way of making money. It has almost no requirement, and is quite profitable. (Depends on what you are cutting). A more detailed guide on this can be found here

Trivia
The amount of coins you get for cutting any type of gem is random. You can earn 100 coins up to 8500 coins for each gem you cut.