Quartzite is a hard no foliated metamorphic rock composed almost entirely of quartz. It forms when sandstone rich in quartz is altered by heat and pressure. These conditions recrystallize the sand grains and the silica cement that binds them together. This results in a network of interlocking quartz grains of incredible strength.
The interlocking crystalline structure of quartzite makes it hard, tough and very durable. This is a characteristic that separates true quartzite from sandstone.