Currently Quartz Block is 19k in the shop per stack 2 things, 1st, It is the wrong block. It is Smooth Quartz, Rather then Block of Quartz, And thusly cannot be crafted into anything, such as Stairs / Slabs. 2nd, There is no need for it to be 19k. I can understand it somewhat due to the price of 1 stack of quartz, But quartz blocks cannot be converted back into regular quartz and is mainly just used for making buildings. It is less rare then a mesa biome so shouldnt be over 6 times the price of that block.
