To get Fire Quartz in Stardew Valley, the primary method is to forage it in the Mines starting at floor 80 and above, where it begins to appear instead of regular Quartz. It can also be found in the Skull Cavern, inside Magma Geodes or Omni Geodes, fishing treasure chests, and through panning. Additionally, after reaching floor 80 in the Mines, occasional Fire Quartz may also be found in garbage cans around Pelican Town or purchased once during the Feast of the Winter Star event from Pierre's booth. Here are the methods summarized:

• Forage Fire Quartz in the Mines at floor 80+ or in Skull Cavern.
• Break open Magma or Omni Geodes at Clint's to possibly get Fire Quartz.
• Find it in fishing treasure chests or by panning.
• Occasionally found in garbage cans after reaching floor 80.
• Bought once per year at the Feast of the Winter Star from Pierre.

Fire Quartz can be used for the Community Center's Geologist bundle, crafting Slime Egg-Press, making refined quartz, tailoring a red shirt, and completing some quest requests.