Nether Quartz

Nether quartz or simply Quartz is a Nether exclusive item.

Mining
Nether quartz ore mined using a pickaxe will drop one unit of nether quartz. If the pickaxe is enchanted with fortune, it may drop an extra unit per level of fortune, up to a maximum of 4 with Fortune III. If the pickaxe is enchanted with silk touch, the ore will be dropped.

Nether reactor
In Pocket Edition, nether quartz is only obtainable through the nether reactor.

Video
Note: The video does not show a crafting recipe for Granite and Diorite, this was before they were added in 1.8.