Quartzite is a useful resource in Grounded. You can use it to make a dew collector or a repair tool to repair your partially broken or damaged structures that come under attack against the giant bugs patrolling near your camp. The walls protecting you around your home won’t last forever, and it can be incredibly annoying having to always rebuild them without the repair tool. Having plenty of quartzite at your campsite is useful, but to find it, you need to explore underground.
You can find it by looking for any caves in the backyard, and dark places where you need a torch to see anything. An excellent spot to start looking is at the location where you have to find out what is weakening the laser after inspecting the mysterious device. The wire goes underground, and if you follow it, you can find plenty of mites and quartzite at the bottom. You do need to use a pebblet hammer to crack open the resource to access more of it, so make sure to have one in your inventory.
When you return with quartzite back to your camp, make sure to use the analyzer to learn about the several crafting options that you can use with it. The dew collector is an excellent addition to your camp to passively collect water. You can place it in storage chests to keep it safe.