Diamond ore is a mineral block generally considered to be one of the most valuable and elusive blocks in the game (although not as rare as emerald ore). When mined with an iron or diamond pickaxe, it drops one diamond (1-4 with a pickaxe enchanted with Fortune III), as well as experience orbs. The diamond ore block itself can be obtained by mining the ore with an iron or diamond pickaxe enchanted with Silk Touch.
Diamond is only found in the lower 16 blocks (above bedrock), though statistically, the levels to find the greatest amount of Diamond Ore are levels 8-12. Even though Diamond Ore is also common on lower levels, these lower levels have a greater chance of lava pools, which can pose as a serious threat.