Ore

Ore is a block type in Minecraft. Ores are primarily collected for crafting purposes, such as pickaxes, shovels, and more. Redstone ore is used as a type of "wiring", which can be used to create redstone circuits, compasses and watches. Ore can also be combined to create a block of the material type. Blocks are expensive, requiring nine of each ore to create, and are mainly recommended for storage purposes.

Availability
In Minecraft Alpha, coal ore can be found up to layer 127 (number of blocks above the void, which is under the lowest bedrock layer), iron ore can be found up to layer 64, gold ore can be found up to layer 32, and diamond ore can be found up to layer 16.