There are quarries of quartzite in New England and in the Piedmont Plateau farther south. There are deposits in the rocky regions around Lake Superior and in the western mountains. This tough mineral is often ground and used to make glass and deposits occur in widely separated places where ancient mountains have been pressed and heated to form metamorphic rocks.

The basic mineral in quartzite is quartz, which starts out as gritty grains of sand. The hard grains become cemented in softer minerals to forrz sandstone. Heat and pressure in the earth’s crust turn the sandstone into quartzite. We find grades of sandstone in the process of becoming quartzite and we may have to crack open a specimen to tell which is which. Sandstone breaks or cleaves between its gritty grains. Quartzite is hard and compact enough to crack clear through its grains of quartz.