Gravel

Gravel is a type of block typically found in naturally occurring pits, underwater, underground or in The Nether. Like Sand, Gravel will fall to the lowest y-coordinate below it if there is no block underneath it. Therefore it is possible to suffocate with careless use of gravel by being crushed beneath the weight. If the lowest block in a column of Gravel is occupied by a nonsolid object, like a Torch, the Gravel block will disintegrate into a gravel resource instead.

In Alpha and Beta, gravel has a 10% chance of dropping flint once destroyed. However, this has been increased since Beta 1.3. Flint is used to create Flint and Steel and Arrows. Gravel blocks that don't drop flint can be picked up, placed, and destroyed again. However, blocks that drop flint do not drop gravel, so this cannot be exploited to gain an infinite amount of flint. Shovels will destroy gravel more quickly than other tools, but do not affect the chance of flint being dropped.

Uses
Gravel's abundance and gravity-obeying property makes it useful for a variety of tasks, especially considering the other gravity-aware block Sand is more useful for creating Glass. For exploration, they can be used to quickly build pillars to reach heights that are easy to dismantle after. They can also be used to quickly fill in water or lava lakes by dropping them on the edges or against overhead blocks, so that they fall and occupy the fluids.

Filling caves in with gravel is also a quicker way to close them off after mining them while preventing hostile mobs spawning. Finally, it can be dropped from above onto trapped mobs to suffocate them to death.

Power-mining
A great way to power-mine massive columns of gravel is to dig under the stone or dirt that it is resting on. Under that dirt or stone, place a torch, a redstone torch, a piece of redstone wire, or a piece of minecart track. Mine the dirt or stone and the column falls into the placed object, quickly producing dropped resources. This can also be used for Sand.

Trivia

 * On occasion, some normally generated maps may produce beaches made of gravel instead of sand.
 * Gravel spawns in 2 block high bands across the walls of the Nether.
 * In the Nether, it is possible to find massive cliffs made of naturally-floating gravel. Just like with Sand, if you destroy, replace, remove, or if a Ghast's cannon ball hits any of these blocks, all of the adjacent floating blocks will collapse.
 * An old glitch in Classic mode allowed players to raise the height of a fluid block by placing Gravel (or Sand) over it. The Gravel would stay suspended in mid-air until it was broken. When broken, a fluid block corresponding to the type below the Gravel would appear where the block was. The suspended fluid block would remain immobile until a block was placed next to it, causing a flood. This bug has since been fixed.
 * If a flint is found from destroying a gravel block, a gravel resource will not be released.
 * Dirt adjacent to gravel is usually 2 or more blocks high.

Gallery
Kies Grind Żwir