Nether Quartz

Nether Quartz is a Nether exclusive item obtained by mining Nether Quartz Ore. This item had been added in snapshot 13w01a            and will be released in the Redstone Update (1.5.1). Nether quartz are the essential ingredients to create redstone comparators, daylight sensors, and the Block of Quartz.

Ore
The Ore is an only available in the Nether. When mined with any pickaxe, it drops a Nether Quartz crystal, which can be used to make a Comparator and a Daylight Sensor. Like Coal, Redstone, Diamond, Emerald and Lapis Lazuli Ore, Nether Quartz Ore drops experience when mined, and works with both Fortune and Silk Touch enchantments.

Nether Quartz seems very abundant, but is actually about as abundant as iron in the overworld. It simply looks like it is more abundant, because you can see more netherrack, but in caves in the overworld you cannot see as much surface area. It is also available at any layer. In reality, there are an average of roughly 70 ores per chunk.