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 than 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 fall on him. There also was a glitch in an old version of singerplayer Creative mode for a while, that caused a flood if water was placed on a wall with blocks affected by gravity. This bug is now fixed.

Minecarts prevent Gravel from falling.