Quartzite
Quartzite
(from German Quarzit, not to be confused with the mineral quartz, is
a hard, metamorphic rock which was originally 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. Quartzites often occur in various shades of pink and red
due to varying amounts of iron oxide. Other colors are commonly due to
impurities of minor amounts of other minerals.
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.
Orthoquartzite is a very pure quartz sandstone composed of usually well
rounded quartz grains cemented by silica. Orthoquartzite is often 99%
SiO2 with only very minor amounts of iron oxide and trace resistant
minerals such as zircon, rutile and magnetite. Although few fossils are
normally present, the original texture and sedimentary structures are
preserved.
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.
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