Redstone Ore

Redstone ore is the ore block from which redstone is obtained.

Obtaining
The redstone ore block itself (rather than its redstone drops) can be obtained by mining it with an iron or diamond pickaxe with the Silk Touch enchantment.

Natural generation
Redstone ore veins form at the bottom 16 layers of the map. Below layer 14, it can be found in 1.025% of stone. There are an average of about 24.8 redstone ores per chunk.

Redstone ore forms in veins made up of 4 to 8 blocks. However, multiple veins together or non-stone surrounding the vein can change those numbers.

Usage
Redstone ore drops 4 to 5 redstone and 1-5 experience when mined with an iron pickaxe or better. Mining with a Fortune enchanted pickaxe will increase yields.

Light
Redstone ore will produce light (strength 9) and red particles when clicked, updated, or contacted by any mob (including the player, if not sneaking). This effect will continue until the redstone ore block receives a block tick (averaging 47 seconds). This effect does not actually produce redstone power, but the block changes can be detected with a block update detector allowing redstone ore to act like a pressure plate for mobs, but capable of detecting contact with its sides and bottom surfaces as well.

Smelting ingredient
Smelting the ore instead of mining it is highly inefficient, as mining the ore block yields 4 to 5 redstone rather than the single redstone that smelting yields.

Trivia

 * Redstone ore can be found in Pocket Edition and can be mined but the dust has no use yet except for making clocks, compasses, and powered rails.
 * In Minecraft Pocket Edition, stepping on redstone ore does not cause a block update.