Quartzite

Metamorphic rock composed of firmly cemented quartz grains is what quartzite termed as. Most often it is white, light gray, yellowish, or light brown, but is sometimes colored blue, green, purple, or black by included minerals. It results from the metamorphism of pure quartz sandstone. Most easily distinguished from sandstone quartzite fractures across constituent grains of sand. Quartzite is very resistant to chemical weathering and often forms ridges and resistant hilltops. The nearly pure silica content of the rock provides little to form soil from and therefore the quartzite ridges are often bare or covered only with a very thin soil and little vegetation. Because of its hardness sometimes is used in the construction of railway ballast as well.