Slab

Slabs are half-blocks that were used to create stairs and certain decor before the actual stairs. Before other updates, these were also used to keep floors from catching on fire. Unlike stairs, slabs do not stop the player's sprinting, which makes vertical elevation equally quick and horizontal speed twice as fast as stairs while sprinting on slabs. Upside-down slabs occupy the top half of their block space rather than the bottom half. To place a slab upside-down, right-click on the bottom of a "ceiling" block, which can be removed after the slab has been placed, or by right clicking the top half of another block, if you wish to place it on the side of another full or half slab block.

All six types of "stone" slab have the same data values; like wood and colored wool, they are differentiated by their damage values: stone slabs have a damage value of 0, sandstone slabs are 1, "wooden" slabs are 2, cobblestone slabs are 3, bricks are 4, and stone bricks are 5. Damage value 6 is occupied by another, identical stone slab, but with a slightly different double slab form. Upside down slabs have these damage values: stone have 8, sandstone have 9, wooden have 10, cobblestone have 11, bricks have 12 and stone bricks have 13.

Real wood slabs use a different set of block and damage values.

Occurrence
Stone slabs can be found naturally in NPC 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 wells and desert temples.

Crafting
Slabs can be made from three wooden planks or three stone, cobblestone, sandstone, brick, or stone brick blocks, producing six slabs per crafting operation. There also is a stone slab which only uses the top texture of the normal stone slab, but it can't be crafted. The damage value is 6. 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. Currently Netherrack slab and Nether brick slab not exist.

Behavior
Like other partial blocks, slabs are treated as a whole block with other blocks, such as dirt, stone, and glass, and liquids. Two slabs of the same type (e.g. two stone slabs) can be placed one on top of the other to make a single full-size block, but different slab types cannot be mixed in this way. Sandstone, wooden, and cobblestone double-slabs look exactly the same as their full block counter-parts, but take a longer time to break and drop two slabs. Wooden slabs are collected more quickly with an axe and are affected by fire.

An unusual property of slabs is that they are non-solid to redstone. This allows one to hide the redstone wiring in a slab covered channel, while still being able to connect to the wire on the side of the slabs.



Mobs can spawn on top of upside down slabs as of 12w26a, they should spawn on double slabs.

Due to the way blast rays propagate from an explosion, slabs provide extremely effective absorption to explosions taking place directly on top of them. Specifically, this is because explosive entities will be lower in elevation when they explode on top of slabs than they would otherwise be on an ordinary block. Although the few slab(s) directly under the explosion will absorb the full force of the blast (with a resistance of 30) as usual, the propagation of damage to the sides will be greatly reduced. If source of the explosion is elevated for any reason at the time of the blast, this protective quirk is lost.

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.

Bugs

 * Sandstone slabs do not break as fast as normal sandstone blocks do.
 * Sprinting on slabs always makes gray particles, even if one is sprinting on wooden, sandstone or brick slabs.
 * Upside-down slabs are dark when there is a block above it. A normal block beside will emit some light, but the upside-down slab itself will emit no light.
 * Mining a wooden double slab with a pickaxe enchanted with Silk Touch will make it drop only one slab.
 * Due to lighting glitches with the slabs, wheat will be automatically harvested when surrounded by slabs of any kind.
 * Slabs placed directly on top of ice will still give the player the "gliding" effect. The Player may also sprint jump on top of the slabs in order to receive the faster sprinting effect.
 * Wooden slabs placed prior to Minecraft version 1.3.1 are treated as stone slabs, as they need to be harvested with a pickaxe.
 * In creative, when you use pick block on any type of upside-down slab in minecraft 1.2.5, you get a similar looking slab that places itself upside down no matter how you place it. This slab doesn't stack with its regular form.
 * Zombies and skeletons don't burn in sunlight if standing on single lower slabs.
 * In creative, when you pick block any double slab without the slab in your inventory, you'll get a stone slab back. If you have any slab in your inventory, you'll scroll over to the first slab from the left, even if it's not the correct type. Note this doesn't happen when block picking single slabs.
 * Sometimes in multiplayer, you'll place a normal slab, when clicking on the side of an upside-down slab.