Flint

Flint is an expendable object found by quarrying Gravel. When destroying gravel blocks, you have a 10% chance of harvesting flint instead - this figure is taken directly from the source code. Some players have realised the ability to place stacks of unwanted gravel then power-mine them in the hope that they can gather more flints. Of course, this usually reduces their stash of gravel by around 10% each time, and there is no way to revert flint rocks back into gravel blocks.

Blocks affected by gravity can be harvested quickly by placing a Torch on a solid block below, then allowing the entire stack to tumble onto that. However, this tactic will not yield flint; you must manually mine gravel if you wish to increase your supply.