In true metamorphic quartzite, also called
meta-quartzite, the individual quartz grains have recrystallized along with the former cementing
material to form an interlocking mosaic of quartz
crystals. Minor amounts of former cementing materials,
iron oxide, carbonate and clay, are often recrystallized and have migrated under the pressure to
form streaks and lenses within the quartzite.
Virtually all original textures and structure have
usually been erased by the metamorphism.
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 (about 7 on Mohs' scale of
mineral hardness), crushed quartzite is often used as
railway ballast. In the United States, formations of
quartzite can be found in eastern South Dakota,
southwest Minnesota, the Wasatch Range in Utah, and as
resistant ridges in the Appalachians and other
mountain regions. The town of Quartzsite in western
Arizona derives its name from the quartzites in the
nearby mountains.
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Granite