Diamond Ore

Diamond Ore is generally considered to be the most valuable and elusive block in the game. It can be mined for a diamond gem using an Iron or Diamond Pickaxe.

Uses
Diamonds can be used to make Shovels, Pickaxes, Axes, Swords, and Armor of the highest quality. It is also a requisite ingredient in Jukeboxes, and solid diamond blocks.

Prospecting
Diamond Ore can be found in veins of 2-8 blocks (sometimes up to 16 if two veins happen to spawn together, and down to 1 if the block that was supposed to be diamond ore is occupied by a cavern or a dungeon). Diamond shows up at elevations ranging from 1 to 20 blocks above the bottom of the map.
 * Below elevation 18, it occurs in roughly 0.12% of rock. Which means you would need to dig 833.33 blocks below level 18 before you are guaranteed 1 diamond ore.
 * This calculates to approximately 4 diamond ore per chunk.

Trivia

 * When diamond was first introduced, it was called emerald.
 * If diamond ore is obtained via inventory hacking, smelting it will give the diamond gem.
 * Diamond, like other ores, is easier to find in caves and empty lava pools, as this gives more surface area.
 * Like other ores, diamond was about 50% more common in the quadrant south-west of the point (0,0) compared to the north-east quadrant. However, this was fixed in Beta 1.6.
 * In some vein formations, ores connect diagonally. Therefore it is recommended to mine around diamond ore. This also permits checking for lava.
 * Diamond Ore, along with other ores, appears in the background on the achievement page.
 * Diamonds are considered to be the rarest item in the game, but, due to a bug in 1.6 (and only 1.6), Clay was the rarest material in the game.
 * Diamond ore cannot be found or placed in Classic as of version 0.30.