Quartzite is a non-foliated metamorphic rock composed almost entirely of quartz. It forms when a quartz-rich sandstone is altered by the heat, pressure, and chemical activity of metamorphism. These conditions recrystallize the sand grains and the silica cement that binds them together. The result is a network of interlocking quartz grains of incredible strength.
The interlocking crystalline structure of quartzite makes it a hard, tough, durable rock. It is so tough that it breaks through the quartz grains rather than breaking along the boundaries between them. This is a characteristic that separates true quartzite from sandstone.
Quartzite, with a Mohs hardness of seven along with greater toughness, is getting more popular in architectural uses. It stands up very well to abrasion in stair treads, floor tiles, and countertops. It is very resistant to most chemicals and environmental conditions. It is available in a range of neutral colors.