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.