Minecraft wiki entry for Nether_Quartz_Ore, associated text: Nether quartz ore can generate in the Nether in the form of blobs. Nether quartz ore attempts to replace netherrack 16 times per chunk in blobs of size 0-24, from levels 10 to 117, in all Nether biomes except basalt deltas. In basalt deltas, Nether quartz ore attempts to generate 32 times per chunk as there are fewer valid generation areas.