Nether Quartz

Nether quartz, or simply quartz, is a smooth, white mineral found in the Nether.

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 four with Fortune III. If the pickaxe is enchanted with silk touch, the ore will be dropped.

Trading
Expert-level stone mason villagers buy 12 nether quartz for an emerald as part of their trades.

Trivia

 * All of the sensor related items that are craftable (comparator, daylight sensor, observer) are crafted with some nether quartz involved.