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. Nether quartz are the essential ingredients to create redstone comparators and daylight sensors.

Blocks made from Quartz
Jeb_ released a image showing 3 "(milky) quartz block tests"

Trivia

 * Mining Nether Quartz provides quick and easy experience since it provides ample experience orbs and is easier to find. (Taking into consideration the risks involved of being in the Nether.)