Nether Quartz

Nether quartz is a Nether exclusive item obtained by mining nether quartz ore. Nether quartz can be obtained in the Pocket Edition when it is spawned by a Nether Reactor, although in the Pocket Edition its only use is to craft smooth quartz blocks.

Smelting
Note that the nether quartz ore block cannot be obtained without the Silk Touch enchantment, and that this smelting is slightly inefficient because with Fortune, you can get more than one quartz per ore. Also, there would be no reason to collect it with silk touch if you were just going to smelt it as it would be more efficient on long excursions to save space and to gather the experience gotten from mining the quartz ore for later.

Trivia

 * Nether quartz appears to be quite common, 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 that netherrack can be removed far more quickly than stone.