Slab

Slabs are blocks that allow the player to change elevation without jumping. They are not as compact as stairs, requiring twice the horizontal space for an equivalent change in elevation. Stone slabs have been in the game from Classic, whereas sandstone, wooden, and cobblestone slabs were added in the Beta 1.3 update.

All four types of 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, and cobblestone slabs are 3.

Crafting
Slabs can be made from three wooden planks or three stone, cobblestone, or sandstone blocks, producing three slabs per crafting operation.

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 have the same texture as sandstone, wooden planks, and cobblestone, respectively.

Due to a bug, wooden slabs can currently only be collected with a pickaxe, and upon breaking, a wooden slab produces the stone slab's particle effect. This is likely due to the fact that the slab types are differentiated by their damage values instead of by different data values, similar to wood and colored wool.

History
Stone slabs were first introduced in Classic mode. In Classic and Survival Test, stone slabs could be obtained by mining a coal block because of the lack of inventory and crafting.

Stone slab blocks were called stair blocks before the current stairs were added; then known as steps (the two forms being single steps and double steps) before all items got official names upon the Beta release.

Before the additional slabs were added, a double Stone Slab would only yield one slab when broken. Since the Beta 1.3 update, all double slabs yield 2 of their respective single slabs when broken.

Before Beta 1.3 came out, stone slabs were made with cobblestone instead of stone, but that update introduced cobblestone slabs to the game and changed the recipe for Pressure Plates and stone slabs so that there wouldn't be any conflicting recipes.

Trivia

 * Despite the fact that sneaking gives a player an apparent height of 1.5 blocks, doing so does not allow the player to walk over a single slab with only a single empty block above it.
 * A player can not walk from a block of soul sand to a stone slab without jumping.
 * If you put two stone slabs next to each other in water, you can place a ladder on the stone slab (which is otherwise impossible). However, any ladder placed in this way is invisible.
 * Single slabs have the tendency to let through arrows shot from above.
 * Single slabs will destroy gravel and sand blocks that fall onto them.
 * Being pushed onto a slab by water will force the player to jump.
 * Double slabs cannot be made when there is a block above the single slab. Only single slabs can be placed in one-block-high gaps.
 * Single slabs are marked by the game as transparent, even though they affect light like a regular solid block. Thus, single slabs do not cause suffocation and you cannot place torches or other fixtures on them.

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