Quartzite

What is written on the plate:

Quartzite

The quartzite consists almost entirely of quartz and a few feldspars. During metamorphism, the fine-grained clasts were transformed with the surrounding cements into a non-porous quartz rock. The quartzite is part of a sequence over 300 m thick that is widespread in Western Europe and North Africa. It originated as beach and shelf sand in a shallow sea on the northern edge of Gondwana. The red coloring goes back to Permian weathering.

Upper Frauenbach Quartzite, Lower Ordovician,
Steinheid, Thuringian Slate Mountains, ca. 500 Ma

Quartzite

Location: Steinheid, Thuringian Slate Mountains

Age: 500 million years

Quartzite is a fine to medium-grained metamorphic rock composed primarily of quartz. With a quartz content of at least 98 percent, quartzite is characterized by its high resistance to environmental influences. The term quartzite is also often used for sandstone, which becomes as hard as real quartzite through silicification. A rare variety of quartzite is the flexible itacolumite or jointed quartz.

In many cases, pure quartzite has a white-grey or white color. Yellow and red colors are caused by iron minerals, while magnetite and pyrite impurities can sometimes result in a brown or gray tint. There are also varieties of quartzite with colors such as dark green or gray-blue. Quartzite consists primarily of interconnected, recrystallized quartz grains sintered at grain boundaries by pressure solution.
Depending on the degree of metamorphism, quartzite can be very hard and brittle, while weakly metamorphic quartzites can exhibit lower abrasion and frost resistance. In some cases, sedimentary structures of the original rock, such as ripple marks or cross bedding, may also have been preserved.

Quartzite is usually formed from sandstone metamorphism, but it can also be formed from chert, radiolarite, or chert. Under the influence of pressure, temperature and mechanical stress, the quartz grains in sandstone are deformed by the pressure solution and their crystal lattice begins to rearrange. The quartz grains grow beyond their original grain boundaries and form a densely networked structure. The original pore spaces and the sedimentary structure largely disappear. If clay components are present in the parent rock, mica minerals such as muscovite or phengite are formed. Dumortierite or kyanite can give quartzite a bluish tint.

Quartzite is used in various fields because of its hardness, durability and attractive color variations. Because of its compressive strength and resistance to weathering, quartzite is widely used as a building material for interior and exterior siding, flooring, stair treads, paving and facades. It is also used in landscaping for walls, paths and decorative elements.