Gravel

Gravel is a type of block typically found in naturally occurring pits, underwater, on beaches, or in The Nether. Gravely beaches are scarce, and gravel in The Nether is more scarce.

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 surrounded by it. 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. 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, if a gravel block drops flint, it does not additionally drop a gravel block, preventing the creation of an infinite amount of flint. Flint can be obtained from gravel with any tool.

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, it 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 quick way to prevent mobs from spawning. Mobs can also be suffocated with gravel.

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, a Pressure Plate, or a piece of minecart track. Mine the dirt or stone and the column falls into the placed object, quickly producing dropped resources. Note that this method will not generate flint. This can also be used to mine Sand.

Trivia

 * 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 fireball 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.
 * Dirt adjacent to gravel is usually 2 or more blocks high.

Gallery
Kies Grind Żwir