Sand

Sand is a block naturally found on coasts and desert biomes, generally in four-block-deep layers supported by stone and sandstone. Sand blocks can be mined easily by hand or with shovels and drop as resources regardless of the tool used. Sand has a very low blast resistance.

Behavior
Sand, if there is no block below it, will turn into falling sand and fall until it lands on the next available block, thus making it one of five blocks (as of 12w41a) to which gravity applies (the others being gravel, TNT (turns into primed TNT), anvil (as of 12w41a), and the Dragon Egg). This will happen even if the block of sand is attached to a sticky piston, as the piston will only stick to a block when retracting. When sand is being affected by gravity and falling, it exhibits a smooth falling animation. If falling sand lands on a mob or the player and covers their head, it will suffocate them until they successfully destroy the block, move out of the block or die. If falling sand lands in the space occupied by a non-solid block, (such as torches, slabs, rails, or Redstone), it will drop and turn into a sand resource block. If falling sand falls into lava, it will catch fire (since it's an entity) but still lands and piles up like normal if the falling distance is short. When the sand becomes a block again, the fire goes out; otherwise, the falling sand block burns up/disappears while falling. Also, if it falls onto a cobweb it will slowly fall until it has gone through it completely, or until it touches the ground, at which point it will turn into a resource block. Placing a block of sand into the space directly above a non-solid block will not cause it to turn into Falling sand. Sand blocks can be suspended in indefinite defiance of gravity in this way, most famously using torches. Additionally, if sand is placed anywhere straight up from a painting, it will pass right through the painting as if it wasn't there (the same happens to gravel).

Uses
Sand can be used in the construction of Airlocks and the creation of mob suffocation traps. It is also useful as a scaffolding material in some situations. Being affected by gravity, it can be quickly and easily removed from ground level and can be used to construct a safe path downwards from a higher position (such as a hole directly down through the roof of a large cavern) even if the ground itself cannot be reached by hand.

In addition, sand is used in the production of glass via smelting and TNT via crafting with gunpowder.

Torch mining
When mining a large column/pillar of sand, a good method is to dig under the stone or dirt that it is resting on. Under that dirt or stone, place any partial block (such as a torch, slab or cobweb). Mine the dirt or stone and the column falls into the placed object, quickly destroying the sand. This can also be used to mine gravel. Leaves can break sand/gravel.

Cofferdam mining


If large quantities of sand and sandstone are needed, the ocean floor is a great source of both of these. To create a cofferdam, find a place in a large lake or ocean that is only one or two blocks deep, and fill in that spot to be just above water level. Then dig a pit inside so that the water can't get back in. With a large enough pit, a large chest can be filled with sand and sandstone fairly easily.

This method can also be used in Desert biomes without the need to drain away water.

Bugs
In Minecraft version 1.5 sand, when falling, will spawn the falling sand entity above one block, and turns back into the block before it hits the ground.

Trivia

 * In classic, if the player is next to a set of blocks and places 2 sand blocks above them, using the side of those blocks, they will end up inside of those blocks, with an internal texture identical, but darker than regular sand. Like most blocks, they are also hollow. The same bug happens with gravel.
 * If a block of sand has snow on it and is made to fall, the snow is destroyed and will not drop a snowball.
 * If sand falls onto tall grass, rail, powered rail, flower pot, detector rail, redstone torch, torch, trapdoor, signs, flowers, redstone repeaters, or cobwebs it will break.
 * Because falling sand is considered an entity it can be launched in a TNT cannon, similar to an ignited piece of TNT. The only significant building difference between a normal TNT cannon and a sand cannon is that a piston is needed at the end of a sand cannon. A correctly-timed piston will allow a sand block to fall just before the TNT charge detonates, launching the falling sand entity a considerable distance.
 * There is a bug with this which will duplicate the sand. When using 2 TNT's timed almost after each other and placing the sand in air just before the TNT explodes, the sand will duplicate into 2 sand blocks on impact.
 * Sand will fall at the same rate when submerged in water as it will when in air. This is also true for lava.
 * If a player is standing on a stack of sand or gravel, and the stack falls on a non-solid block, the player will fall fast enough to take damage or even die.
 * Even though 4 sand blocks can be crafted into 1 sandstone, 1 sandstone cannot be crafted into 4 sand blocks.
 * Falling sand entities can be caught inside cobwebs. When falling, the block will be slowed down. If there are more blocks falling into the cobweb than there is room beneath the cobweb for the sand to settle, the sand caught in the cobweb will instead drop as items. This can be used to simulate quicksand.
 * Sand will fall through torches without breaking if there is air below the torch.
 * There is a bug from 1.5pre that when sand placed on a block of air it will move one block up and then falls.
 * The block ID of falling sand can be changed so that when falling it will look like that block and will change into that block when it hits the ground