Doesn't turn into quartz blocks because you can't reverse them back. Do /cnd hand (while holding quartz) or /cnd quartz

 

I would like to point out that you can do /condense all to make quartz blocks with quartz.

 

/condense all will force every item in an inventory to their basic block form whereas /condense will only work with certain types of blocks that do not have more than 1 base function. Well for the most part this is true, although there are exceptions like glowstone dust which has to be /condense all because it has uses other than block form, the same applies to quartz which can be used in potions among other things.