Quartzite is a hard, non-foliated metamorphic rock which was originally pure quartz sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of iron oxide. Other colors, such as yellow, green, blue and orange, are due to other mineral impurities.
Quartzite is one of the most physically durable and chemically resistant rocks found at Earth's surface. When the mountain ranges are worn down by weathering and erosion, less-resistant and less-durable rocks are destroyed, but the quartzite remains. This is why quartzite is so often the rock found at the crests of mountain ranges and covering their flanks as a litter of scree.
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.
In architecture, marble and granite have been the favorite materials for thousands of years. Quartzite, with a Mohs hardness of seven along with greater toughness, is superior to both in many uses. It stands up better to abrasion in stair treads, floor tiles, and countertops. It is more resistant to most chemicals and environmental conditions. It is available in a range of neutral colors that many people prefer. The use of quartzite in these uses is growing slowly as more people learn about it.