Quartzite << KWAWRT syt >> is a rock composed chiefly of the mineral quartz. The quartz occurs both as individual grains and as the cementing material that holds the grains together. Quartzite, one of the hardest rocks, is a common type of metamorphic rock (see Metamorphic rock). It forms when heat and pressure change the grains in quartz sandstone. In this process, called recrystallization, quartz grains become so firmly bonded that any breaks that occur in quartzite go through the grains rather than pass around them.
