Snow Block

Snow blocks are full sized block versions of snow. They are crafted from 4 snowballs, allowing the player to create them through their inventory crafting window. One may not reverse the crafting process, but the block may be placed and destroyed with a shovel, yielding 4 snowballs.

Snow blocks are not destroyed by forces that would realistically melt snow, such as lava, fire, and torches, and are unaffected by water.

Snow blocks have many applications, such as building, decoration, and storing snowballs. They blend in well with the taiga and the tundra (ice plains) biomes, and can be used to build snow-themed buildings, such as igloos or snow castles. Snow may still fall on them, making them look bigger than they really are. They are also sometimes used for playing Spleef. One of the most popular uses is for the production of Snow Golems.

As a crafting ingredient
(Snapshot 13w05a or later)

Snow is also used to make Snow Golems by putting 2 snow blocks vertically and a pumpkin on the top as the head (this is done by stacking the blocks in the world, not in the crafting grid).

Trivia

 * When a snow block is on grass before it turns the grass into dirt the grass changes as if a snow layer was on it (This may have been part of a planned weather feature, such as multi-layered snow, or just a little feature Notch programmed in).
 * Snow blocks can be used in farms that utilize efficiency tools, as snow blocks are unaffected by efficiency enchantments.