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
20-26 Nether Quartz can be sold to stone mason villager for an emerald as their only fourth tiers trade.

Stone mason villagers buy 12 nether quartz for an emerald as one of their fourth tier trades.

Trivia

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