Gravel

Gravel is a type of block typically found in naturally occurring pits, underwater, or underground. Like Sand, gravel will fall to the lowest z-coordinate below it if there is no block under it. Therefore it is possible to suffocate with careless use of gravel. If this lowest block is occupied by a Torch, the gravel block will disintegrate into a gravel resource instead.

In Alpha, it has a roughly an 8.5% (based on testing) chance to drop flint once destroyed, which is used to create Flint and Steel and Arrows. Shovels will destroy this block quicker then normal, like Sand and Dirt. Because gravel is affected by gravity, it was used to make hallways that seal when water touches torches supporting it, creating an Airlock. However, recent changes made means Gravel disintegrates when falling on torches so creating an airlock is only possible with Sand.

Gravel has been added to caves, and is infamous for being capable of suffocating the player if two blocks of it land on them. For awhile in an old version of singleplayer Creative mode, that had a glitch that caused water to flood from blocks affected by gravity if placed against a wall but not on the ground. The bug has since been fixed.

Minecarts prevent Gravel from falling.