The Diamond Pickaxe is a weapon from Naughty Bear: Panic in Paradise. In the Secret Temple of the Retreat and Spa for War Heroes.
The Diamond Pickaxe, like the Pinata Stick, releases money when used for hit something. According to the Narrator it was used for dig out a kind of mineral sugar in the past.
The Diamond Pickaxe was a reference to the game Minecraft, being the highest tier of pickaxes.
The game also references Notch, a creator of said game in the description of the Diamond Pickaxe.