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.

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, and the fact that the Nether has more exposed blocks than an overworld cave.
 * Nether Quartz can be obtained in Pocket Edition (current 0.6.1) when it is spawned by a Nether Reactor. It's only use is to craft Smooth Quartz block.