Nether Quartz

Nether Quartz is a Nether exclusive item obtained by mining Nether Quartz Ore. This item had been added in snapshot and will be released in the Redstone Update (1.5). Nether quartz are the essential ingredients to create redstone comparators, daylight sensors, and the Block of Quartz.

Smelting
Note that the nether quartz ore block cannot be obtained without the Silk Touch enchantment, and that this smelting is inefficient as destroying an ore block yields 4-5 nether quartz (*confirmation required*) rather than the single one smelting does. If a nether quartz ore block is obtained, it is much more efficient to place the block and mine it with a pickaxe without the Silk Touch enchantment.

Trivia

 * Nether Quartz appears to be quite common in The Nether, but in reality, is about as common as Iron Ore in the overworld, each spawning approximately 70 ores per chunk. What makes it seem more common is that it can spawn on any layer within The Nether, combined with the fact that the Nether has more exposed blocks than an overworld cave, and the fact Netherrack can be removed far more quickly than Stone.
 * Nether Quartz can be obtained in Pocket Edition (current 0.6.1) when it is spawned by a Nether Reactor. Its only use is to craft Smooth Quartz block.