Slab

Slabs are half-blocks.

Obtaining
Stone-type slabs require a pickaxe to mine, while wooden slabs can be mined with anything, but an axe is quickest.

Natural generation
Stone slabs can be found naturally in villages lining the roof of a blacksmith shop and inside some of the buildings where they form counters. They are also found in strongholds where they are used in some of the stairs, ledges and torch pillars. Sandstone slabs can be found naturally in desert villages, desert wells, and desert temples.

Crafting
Unlike many wooden items, wooden slabs must be crafted entirely from one type of wood, but by the same token, they keep the type (and color) of the wood used, thus "Birch Wood Slabs" and so forth.

Behavior


Slabs are treated as a whole block by other blocks and liquids. Two slabs of the same type can be placed one on top of one another to make a full-size block, but different slab types cannot be mixed in this way.

Single slabs have the tendency to let through arrows shot from above. Slabs placed on the bottom half of a block will destroy gravel and sand blocks that fall onto them. They cannot cause suffocation, prevent placement of torches or other fixtures on them and chests with single slabs above them can still be opened.

Redstone can be connected to the wire on the side of the slabs. Redstone placed on top of an upside-down slab can receive signals from an adjacent block of redstone one block lower but cannot transmit signals to it. This is why "ladders" made from upside-down slabs, as pictured to the right, can transmit redstone signals up, but not down.

Mobs can spawn on top of upside down slabs and on double slabs.

Due to the way blast rays propagate from an explosion, slabs provide extremely effective absorption to explosions directly on top of them.

Despite how sneaking lowers the player's eye level half a block, doing so does not allow the player to walk over a single slab with one block of air above it because of the player's true height. A player cannot walk from a block of soul sand to a slab without jumping.

Data Values
The slab blocks use IDs and data values to differentiate between types.

Double Stone Slabs

 * Block 43


 * Block 181

The Full Stone, Sandstone, Quartz and Red Sandstone Slabs have a top texture on all sides.

Stone Slabs

 * Block 44


 * Block 182

Double Wooden Slabs

 * Block 125

Wooden Slabs

 * Block 126

Dirt slab


Before stone slabs were added to 0.26, Notch ran a test of dirt slabs. They were never added to the actual game and were only mentioned once. They replaced all dirt blocks and did not grow grass on top.

Trivia



 * Slabs let a small amount of light pass through their edges. This light is only visible with Smooth Lighting is turned on, and does not affect mob spawning or other light-dependent processes.
 * The exception of this is that any light directed through a slab does not affect any block's light values north of the source.
 * Mobs see a slab as a full block. Therefore, by placing an upside down slab above a slab with a block in between, there will be sufficient space for the player to walk through. Mobs, however, will see one block of space in between and won't get through. This does not apply to baby zombies and spiders, because they are only one block tall, and to slimes, as they will hop towards the player even if there is something obstructing the way.
 * Stone slabs are the only slab which, when stacked, do not mimic their block in texture.
 * You can sneak walk off slabs at ground level.
 * Minecarts on powered rails will not be repelled from a slab. They will, however, be repelled by a slab with a minecart on top.
 * If you set a slab on the top half side of any block under water, it will displace as much of it as a whole block. Not only can you grab a quick breath of air, but you can see as clear through the water as looking over the land above the surface than in it itself.
 * When an upside down slab is pushed from the bottom by a piston (or regular slab pushed from the top), it is pushed without having contact from the piston. The same idea can also be made when pulled by a sticky piston.
 * Slabs have a light level of 0, as well as the bottom step of stairs.