This page offers a guide on how to obtain Quartz in My Time at Sandrock.
How to Mine Quartz
Quartz can be obtained by mining gravel rocks found nearby your workshop with your pickhammer. They’re a little bit of a rarer drop but you’ll be able to get a few with just a bit of hard work!
Later on, when you have a stronger bronze pickhammer, you can also obtain it from hard rocks too. And when you have an ore refinery, you can make some in that as well.
How to Make Quartz in an Ore Refinery
Later in the game, you can also obtain quartz from an Ore Refinery. Like the Recycler, the Ore Refinery drops random items depending on the stuff you feed into it. Tin Ore, Copper Ore and Stone all have a guaranteed chance of dropping Quartz!
Quartz can also be purchased at the Ceramic Gate Shop for around 16 Gols each - this is an approximate price as costs in Sandrock fluctuate!