Minecraft wiki entry for Nether_Quartz_Ore, associated text: Nether quartz ore has the same blast resistance as other ores (except ancient debris, which is fully blast resistant), which is more than the quartz block and netherrack combined.
The vast quantities of easily available Nether quartz ore in the Nether, combined with the relatively large quantity of experience gained from digging it, make Nether quartz mining a relatively fast way to level up in Minecraft without dedicated experience farms. Breaking one Nether quartz ore provides 3.5 experience points on average, so breaking about 100 of them raises the player from level 0 to 16, and about 400 from level 0 to 30.
Nether quartz ore is generated as part of the dimension, while netherrack is generated as part of the biome.‌[Java Edition only]
This can be seen, as when a Buffet world with the nether biome is generated, there is netherrack but no quartz ore.
In Bedrock Edition, if the Nether is generated in the Overworld as a biome, neither netherrack nor Nether quartz ore is generated, but the terrain is completely made out of stone with bedrock ceiling.