No problem, I like answering questions about my game!
Quartz can be mined in the Goblin Mines, it is just hidden in a secret room. There are three secret rooms that you can dig up, you can see them marked by "cracks" in the walls! The first two rooms are more obvious, but a third is hard to find it is at the very top right of the mine in the dark wall. Room 1 and 3 have Copper nodes and Room 2 has Iron and Quartz nodes!