Quartzite

Quartzites are fine to medium -grained metamorphic rocks that are defined with quartz contents above 98 percent. They are characterized by relatively large resistance to environmental influences.

The term quartzite is used in many cases not entirely applicable to sandstones whose grains after cementation by silica ( silicification ) are similar to real hard as quartzite. A rarely used name for these rocks is gravel cement quartzite.

Appearance and properties

Pure quartzite has in many cases a whitish-gray or white color, such as the Italian-born silver quartzite. Yellow and red colors are caused by admixtures of iron minerals. The frequently occurring yellow variants are caused by the often existing in the source rocks mineral limonite. Due to impurities of magnetite and pyrite quartzite is sometimes brown or gray, rare colors such as dark green or gray-blue. The mineral Dumortierite or kyanite quartzite colors the blue to blue.

Quartzite consists essentially of interconnected recrystallized crystal grains are sintered by pressure solution at the grain boundaries. Depending on Methamorphosegrad may arise in some cases very hard and brittle rocks at low metamorphic quartzite, however, it may well come to less abrasion and frost resistance. Also, sedimentary structures of the source rock, such as Be preserved ripple marks or cross-bedding.

A rare variety of the quartzite is (due to a high content of phyllosilicates ). Itakolumit flexible or articulated quartz

Another example of quartzite with cross-bedding, Sioux Quartzite ( Precambrian), Blue Mound State Park, Minnesota, USA

Quartzite with ripple marks, Gorges du Guil in the French Alps

Formerly detrital quartz grains with quartz cements in thin section

Formation

Quartzite is created through metamorphosis mostly of sandstone, but also chert, radiolarites or chert are possible as a source rock. Through a combination of pressure, temperature and mechanical stress, the individual quartz grains are thereby deformed by pressure solution, and its crystal lattice begins to regroup. In this recrystallization they grow beyond their original grain boundaries (see the thin section image of former quartz grains) and form a densely crosslinked structure. The original pore spaces and the sediment structure are almost completely gone depending on the degree of metamorphism. Are in the original rock Clay pellets contained arise mica minerals, such as muscovite silvery or greenish phengite. This creates pressure through an aligned direction, the layered structure which can be split. Existing in the original rock organic matter ( carbonaceous shares) are converted into graphite among others. The rest consisting of inorganic substance fossils parts are " broken down " and no longer exist in real quartzites. According to geological research that begins " quartzitic metamorphosis in a burial depth of 600 meters and at 200 ° C".

In addition to color, the cleavage is an important distinguishing feature of quartzite variants. Block quartzite, as it is mined, for example, near Wasa (Sweden), or the blue Azul Macaubas from Brazil, is difficult to split. Fissile quartzites are generally formed by regional metamorphism: orthogonal to the printing direction to form mica, which afterwards pretend as a thin separation layers the direction of cleavage, a process similar to how he runs in the formation of slate. The deposition direction is relevant to the cleavage direction and usability, the frost resistance is not affected.

Occurrence

Quartzite is spread worldwide and in metamorphic overprinted Orogenkomplexen a common rock. Deposits in Europe are about the numerous quartzite deposits in the Alps or, for example, quartzite deposits in Spain ( Cordoba, Segovia), Bulgaria ( Balkan Mountains ) or in Scandinavia. Quartzites occur in many of the ancient cratons, so among other things about the Jebel Uweinat in the East Sahara craton in Egypt, in the São Francisco Craton in Brazil or in the Kaniapiskau supergroup of the Labrador Basin on the northeast edge of the Superior craton in North America. Quartzite is also found occasionally as glacial boulders in northern Germany, they come from metamorphic series in Sweden and Norway. The rocks most commonly used in the natural stone sector of Germany in this group are the Alta Quartzite from Alta ( Norway) and the exclusive and high-priced blue varieties from the State of Bahia in Brazil ( Azul Do Macaubas, Azul Imperial ) and from Scandinavia ( Caribbean Blue ).

Many of the rocks commonly referred to as quartzite are not true quartzites, but solidified by silica sandstones. In Germany such " quartzites " or " rock quartzite " among other things, the Rhenish Slate Mountains are, for example, at the gold mine and in the quarries in the valley Köpperner to find on both sides of the Middle Rhine Valley in the Taunus and the Hunsrück in the Taunus. Other deposits are located in the Eifel, Westerwald and east of it in the Hörre. Furthermore, quartzite sandstone is open to the western Harz; there he is slightly reddish in color and is referred to as field - breaking mountain quartzite. Outside Germany also carry many silicified sandstones the name quartzite, such as in Brittany ( Armorikanischer quartzite ) or the " quartzite " of the Cambrian in the Montagne Noire ( Mur quartzeux ).

A notable example of European decorative rocks of this kind is the sort Schokschinsk from an extraction point on the west shore of Lake Onega. This natural stone has been, inter alia, for the sarcophagus of Napoleon ( Invalides ) and for those on the upper portico of the Lenin Mausoleum in Moscow.

Economic importance and use

Due to its hardness quartzite was already in the Stone Age a fairly good substitute for flint. Many tool finds from this period consist of quartzite, both real and made ​​of hard quartzite, silicified sandstone. The Luebbe stones are two megaliths from the Neolithic period, the origin can be dated to the period around 3500 BC. Your material are local lignite - quartzites.

In Egypt, silicified sandstone, but also real quartzite, widely used in architecture and art. Examples are the coffins of Hatshepsut or of Tutankhamun, which were carved from a large block, or the Colossi of Memnon in the temple of Amenhotep III. in Luxor. The ancient mining areas have been used up to the time of the Roman Empire. There are mainly two localities, at Gebel el- Ahmar (eastern bank of the Nile ) northeast of Cairo and at Gebel Gulab / Gebel Tingar (west bank of the Nile ) at Aswan. At the surveys mentioned in each case several extraction points are detected. It was, inter alia, worked with Doleritwerkzeugen.

Quartzite is now a raw material for crystal processing industry. For normal glass making no quartzite, granite screen but can be used. Quartzite is ground finely used in the manufacture of optical glasses or special filler in the production of a refractory material. Particular importance has quartzite today in the construction sector.

Quartzite natural stone

In particular, as a natural stone will find many quartzites use. Commercially, there are numerous varieties which are sold under its own name.

Quartzite indoors

High density gap quartzites as Alta quartzite found in high stress areas for flooring their application (for example at Leipzig ), usually in natural rough training, rare in polished form. As a kitchen worktop come quartzite block on the application.

The suitability as a decorative building material depends not so much on the mineral composition from, but rather from the metamorphic grade and the pore radius distribution. Wasaquarzit in red and Azul do Macaubas in blue are relatively stable rocks. Pink Quartzite from Brazil is rarely used, since on one hand it may discolor irreversibly damaged by mortar water and absorbs very easily due to the unfavorable distribution of pore radii liquid grime. As with any metamorphic rock, the mineral structure is inhomogeneous. Rocks such as Azul do Macaubas can contain the mineral sericite, which is unstable. With water and CO2 are formed in this and other quartzites white spots that can not be removed. Wet areas should therefore not be performed with this quartzite. Some varieties such as Alta quartzite or Albino Yellow from Brazil, however, are relatively easy to use in the bathroom.

Quartzite in the outdoor area

Again, Alta Quartzite is a very resistant material. The low porosity leads in this quartzite to the fact that from setting Moose on the weather side. Depending on the porosity quartzite certain places may well be blown up by microbiological colonization, freeze-thaw and deicing salt.

Chemical resistance

Generally, the crystals are relatively stable, the coloring components are generally the weak point in terms of the resistance to chemicals. Yellowish quartzites them react very sensitive to salt or phosphoric acid. Hydrofluoric acid attacks generally to quartzites. Sulfamic acid, however, can be safely used for lime removal.

In the alkaline range which is considered almost the same. Universal basic ammonia-based cleaners, which reach a maximum pH of 10.5, do not attack generally quartzites. Highly alkaline products containing sodium or potassium hydroxide, not only damage the crystals, but here again the coloring minerals. Budget as oven cleaners contain harmful high alkalis. The high alkaline calcium hydroxide is one of the mortar, the iron minerals can break. This can be transported to the surface with the water transport free iron that forms there with the oxygen visible iron oxides.

Specifics of Laying

Is the rock at high density, it should be expected that by an adhesive coating on the back of the panel and under certain circumstances is necessary even at the edges. An outline of the mortar bed is not uncommon in high-density quartzites. This is due to the lack of mechanical interlocking of the " cement crystals " on the stone by the almost non-existent porosity. At the other extreme, such as pink quartzite, are chemically discoloration caused by the laying means almost a daily occurrence, but the mortar adhesion is very good. So you should be contacted before a transfer from quartzites safety's sake, the mortar manufacturer. In outdoor areas or on underfloor heating, the temperature expansion is another important factor. Quartzites have the highest expansion in the natural stones used industrially, this should be considered when determining the amount of expansion joints and in the selection of substructure.

Types of natural stone

• Alta Quartzite (Norway, Alta)
• Azul Do Macaubas (Brazil, Bahia)
• Azul Imperial (Brazil, Bahia)
• Kalpetranquarzit ( Switzerland, Valais)
• Masi (Norway, Finnmark )
• Green Rauris ( Austria, Rauris )
• Pink quartzite (Brazil, Bahia)
• Schokscha quartzite (Russia, Karelia )
• Wasaquarzit (Sweden)

Quartzite surfaces

Azul Imperial, polished, 22 × 14 cm, Boquira, Bahia (Brazil )

Azul do Macaubas, polished, 22 × 15 cm, Macaubas, Bahia (Brazil )

Pink quartzite, 23 × 15 cm, Lencois, Bahia (Brazil )

Split tiles from Kalpetranquarzit, Valais ( Switzerland )