Granite

Granite (from the Latin granum " grain " ) are bulky and relatively coarsely crystalline igneous plutonic rocks ( plutonic ), which are rich in quartz and feldspars, but also contain dark minerals, such as mica. The mnemonic " feldspar, quartz and mica, which I will not forget ever three " gives the composition of granite again simplified. Granite is similar in chemical and mineralogical composition of the volcanic rhyolite. Granite usually occurs massive and can by horizontally and vertically oriented fractures ( three-dimensional fracture networks ) may be decomposed into blocks, rare granite near the upper boundary of the intrusion is formed platy.

• 4.1 Composition
• 4.2 Related rocks

• 5.1 granite deposits in Central Europe
• 5.2 soil formation and weathering

• 6.1 Overview
• 6.2 Rules for use in construction
• 6.3 types of natural stone (selection)

Terminology and delimitation

In colloquial language the word granite is often used as an umbrella term for various rocks that are similar in terms of their color, texture, grain size, chemical composition, their mineral composition and their formation more or less. Apart from the actual granite and Alkalifeldspatgranit it involves other plutonic rocks, mainly to granodiorites and tonalites and to monzonite and diorite. These rocks, inasmuch as they have a quartz content of more than 20%, combined petrographic under the headings granitoids or granitic rocks. Monzonite and diorite have less than 20% quartz and should therefore be referred to either as " granite " or as " Granitoid ".

Many a time are referred to as "black granites " natural stones. These are usually dark to black ( melanokrate ) hard rock with less than 20% quartz content, the petrographic mostly as Mikrogabbros ( dolerite ), basalts or basanites are classified. Granites are never black - they are among the bright ( leucocratic ) rocks.

In the Valle Maggia and Ticino are very common throughout the " granite " rocks called for roofs, pergolas, road boundaries, tables and benches are used which are not granite in petrographic sense. It is platy paragneiss.

Furthermore, the term granite surfaced repeatedly in phrases. It is thereby directed mainly due to its hardness and resistance:

• " Granite bite " for a futile exercise
• " Hard as granite " for extremely resistant

Formation

General

Granite caused by the solidification of molten rock ( magma ) within the crust, usually at a depth of more than 2 km below the surface. Is in contrast to the volcanic rocks, where the magma penetrates to the earth's surface. Granite is therefore a plutonic rock (technical term: plutonite ). Rocks, (less than 2 km ) solidify very close to the earth's surface, is called, however Subvulkanite, Übergangsmagmatit or gangue, but are often subsumed under the term volcanic. The melting temperature of granitic magmas at atmospheric pressure is 960 ° C, with fluid rich magmas, the melting temperature decreases up to 650 ° C.

Granite arise not from material of the mantle, but from molten material of the lower crust in most cases. For the formation of magma chambers to be reckoned with periods from 10 to 15 million years.

Granite genesis

Classic three granite types are distinguished by Chappell & White (1974 ):

• I-type granites ( igneous source, ie from igneous rocks melted ) are mainly found in ocean - continent collisions, rarely on mid-ocean ridges or hotspots. Mineralogical they are often characterized by a high component of biotite and amphibole ( hornblende fault it ) out.
• S-type granites ( sedimentary source, ie from Sedimentiten melted ) are the result of melting of sedimentary rocks. These rocks are peralumisch why especially Al- silicates such as muscovite (which is why they nicknamed Two mica granite hold ) occur, cordierite or minerals of the Al2SiO5 group herein. They occur especially when it comes to the pressure relief of continental crust, for example through erosion and isostatic rise after the collapse of a mountain range, as was the case in the German low mountain part. By re- crystallization of these rocks get this a new age.
• A-type granites ( anorogenic source, that is, outside of orogenic events or postorogen created ) often occur, the onset of tearing continental crust in appearance. The partially melted crustal Ausgangsmeterial went down probably even before that at least a partial melting ( residuals granulitischer composition after extraction of an orogenic granite ).

Okrusch & Matthes (2009) still add a fourth so-called M-type granite ( mantle source). It is relatively rare occurring Restdifferentiate of mantle melting; this can occur both in oceanic island arcs and at hotspots. Yet recent literature also leads another C-type granites ( charnockitic source). By isotope ratios primarily of strontium the origin and contents of the respective Stammmagmen from the crust and mantle is largely resolved today.

Magmenaufstieg (Intrusion )

Tectonic faults caused by movements of the earth's crust, the magmas serve as easy ways up from the lower to the upper crust. One calls the rise of such magma bubbles up as intrusion. This form in the earth's crust large, often huge Magmenkörper. You can reach considerable levels of several kilometers to several 100 km in length and a corresponding width. This body is called a pluton or batholith.

Tectonic processes, it may be a constriction of the Magmenaufstiegswege. It then creates an isolated magma chamber. But often remain the migration pathways associated with the intrusive body. In addition, however occurs also the case that magmas are stopped during the ascent, as they lose their temperature by the partial melting of the surrounding rock. Often they will still contain relics of unaufgeschmolzenem rock, called xenoliths ( foreign rocks ).

Solidification

Like all plutonic granite also solidifies very slowly at greater depths of several kilometers. According to the melting temperatures of the first crystals begin to form. It possess the dark minerals - the most also have a high density - the highest melting point and solidify first. Only then crystallize feldspars and quartz. The first-formed heavy minerals, such as hornblende or pyroxene, which are excreted due to their higher specific weight and their high melting point in the cooling process earlier, sink to the still liquid residual melt and collect in the lower region of a solidifying magma chamber. Quartz or feldspar, however, accumulate due to their lower density in the melt and in the roof of the magma chamber have often significantly elevated levels. This process is called magmatic differentiation.

Contact the host rock

The contact with the host rock resulted in the edge regions of the magma to " impurities" and to more rapid cooling of the magma. Frequently, arise particularly unusual Gesteinsvarietäten and minerals. This applies, for example on the bluish Kösseine - granite from the Fichtelgebirge, in which it came by mixing the melt with argillaceous host rocks to the formation of fine Mikroklinkristallen which cause the bluish coloration.

Furthermore, the host rock is altered significantly by the high temperature and the supply of material from the hot magma and transformed into a metamorphic rock. The best known example is the horn clif.

After solidification

By further movements of the earth's crust and erosion of the overlying rock then passes the solidified granite to the surface. Here, the granite by tectonic or hydrothermal processes may change significantly. On reaching the Earth's surface also uses the weathering and erosion of the granite itself. With a sufficiently long period of time and warm - humid climate weathering can extend more than 100 m in depth. This process takes place over periods of tens of thousands of years.

Appearance

Generally, granite is medium - to coarse -grained. He has a homogeneous mineral distribution with often directionless texture and the resulting relatively uniform appearance. The structure of granite is characterized by direct grain structure, the size of the crystals varies mostly between 1 mm and several cm. You can see all the crystals with the naked eye usually. In addition to even-grained granites, in which nearly all crystals have the same size class, there are also very often unequal granular or porphyritic granites. There are single crystals, most are feldspars, is several times larger than the crystals of the matrix. A well-known porphyritic granite type is the Rapakiwi.

The color spectrum ranges in granites from light gray to bluish, red and yellow. Play the type of solidification ( crystallization) and environmental factors, which has been exposed to the rock, just as important as the mineral content. The yellow color is weathered granites comes from Eisenhydroxidverbindungen ( limonite ), incurred as a result of weathering influences primarily contained in the granite leading iron minerals.

Color Chart for Granite:

Mineral constituents

Composition

Granite consists mainly of quartz, feldspars and dark, mafic minerals which occupy about 20-40 % of the mass. Mostly it involves biotite (dark mica ), rarely to amphiboles and other mafic minerals. Addition occurs muscovite, the muscovite. The feldspars of the alkali on the plagioclase predominates. As accessory minerals ( minor components ) they lead zircon, apatite, titanite, also magnetite, rutile, ilmenite or other ore minerals, which may originate from zones overprinted in part.

Granite often have a natural radioactivity, as they may contain traces of uranium, rubidium, and other radioactive elements. Another possible carrier of radioactivity are found in feldspars and micas the radioactive isotopes of different elements, especially potassium. The strength of the radioactivity itself can vary greatly within a geological exploration.

Related rocks

Closely related to the granite plutons and often associated with this, there are other igneous rocks, but which have an altered chemical composition. These include the alkali granite ( plagioclase is largely absent ), granodiorite ( plagioclase predominates over potassium feldspar ), the diorite ( K-feldspar is largely missing ) and frequently also pegmatites which almost do not differ sometimes only texturally and chemically from the granite.

In addition, granite is the corresponding plutonic rock of the volcanic rocks rhyolite and obsidian. All three are acidic rocks, ie they have a high SiO2 content, and differ only by their rate of crystallization and, with them, the stone structure and the chemical structure.

Occurrence

Granites are the most common rocks in the continental crust. They are found on every continent. They arise in the context of plate tectonics, primarily in the mountains or at subduction zones: The subducting ( oceanic ) plate also leads sedimentary material with them that can not be subducted, forming the so-called accretionary prism. This can occur granitic magma by the high water content, which forms on cooling the Earth's interior granite.

Granite deposits in Central Europe

• Alps; only partially represented, such as the Aar Massif ( Grimsel Pass), Gotthard massif, Mont-Blanc-/Aiguilles-Rouges-Massiv, Bergell, Ivrea Zone, near Brixen in South Tyrol ( Brixen granite);
• Bavarian Forest
• Erzgebirge; Kirchberg Bergen granite massif, Eibenstocker granite
• Fichtelgebirge; Kösseine
• Resin Brocken area
• Lausitz; there but mostly granodiorite
• Upper Palatinate Forest
• Odenwald
• Black forest
• Thuringian Forest
• Upper Austria, Waldviertel the Bohemian Massif in Austria
• Iron Mountains, Bohemian Massif, Jizera Mountains in the Czech Republic
• Giant Mountains in Schreiberhau, Strehlener granite massif granite massif Striegau - Zobten in Poland
• Vosges Mountains in eastern France ( Alsace and Lorraine )

Granite can also be found very often as glacial sediment in the Pleistocene lowlands of Central, Northern and Eastern Europe.

Soil formation and weathering

Due to their high quartz and Feldspatanteils and their climatically more unfavorable position in the low mountain ranges, occur in Central Europe from granites generally nutrient-poor soils, which also tend to acidification. Depending on the water supply and development depth of soil is usually found Ranker or brown earths, podzols rare. Most of these soils are used for forestry.

In the weathering of granite, a sandy material, which is granite screen (also granite greeting ) called arises. This is also suitable as a building material ways, additive for lime mortar and can be used in earthworks and foundations as a seal. Granite screen you won, for example, a long time from the occurrence of the Bergen massif in the Vogtland and used it in the region as a way, construction and abrasive sand. The Vergrusung takes place there in a thickness of up to several meters.

Use

Overview

Granite have because of their high resistance, hardness and weather resistance, and because of their good grinding and polishing of great economic importance in the construction industry, but are also used in special areas of mechanical engineering, tool making and measuring equipment. They can be found:

• In road construction as paving stone, kerbstone, paving stone, gravel, Bollard
• In railway construction as gravel
• In construction as external wall cladding, flooring, monument, grave stone and shingle
• In interior design as wall cladding, stairs and flooring, window sill, table top, kitchen countertop, vanity
• Horticulture as paving stone, discount stone, fountains, bird bath, etc.
• In technology and science as vibration and wärmedehnungsminimierte disk or optical bench, for marking plates, surface plates etc.
• In sport than curling stone

Granite is used since ancient times in the stone sculpture. Since it is in working technical sense is a hard rock and manual techniques are used in the formation that require a high level of physical and technical effort, granite sculptures are less common than those from soft rock.

Rules for the use in construction

The following is a typical requirement profile technical values ​​with European test standards listed for loaded areas:

• Water consumption according to EN 1925: < 0.32 weight percent
• Compressive strength according to EN 1926: > 160 N / mm ²
• Flexural strength according to EN 12372: > 13 N / mm ²
• Abrasion according to EN 14231: <6.5 cc
• Frost resistance according to EN 12371
• Salt resistance according to EN 12370
• Real density and apparent density according to EN 1936: 2800 kg / m³

Coarse-grained granites have lower pressure and medium-grain Biegezugwerte than the fine to. Stored minerals can cause discoloration.

In the yellow-colored granites to hematite has transformed into limonite. This process has taken place close to the surface in nature over tens of thousands of years and can take place in case of wrong use mortar within short periods. It may well be that also the yellowing of the Granite has completed punctually by a conversion of the feldspar and biotite.

Types of natural stone (selection)

Granite is sold in many types of natural stone, including

• Epprechtstein granite ( Epprechtstein, Fichtelgebirge )
• Flossenbürger granite (Oberpfalz, Bavaria )
• Kösseine granite ( Kösseine, Fichtelgebirge ): The only Blue Granite in Germany
• Mauthausnerstraße granite from Mauthausen, Upper Austria and the other quarries in Bohemia, Moravia, Bavaria and south of the Danube
• Quimbra of the southeastern coast of Småland
• Raumünzach granite ( Forbachgranit, Northern Black Forest, Baden- Württemberg)
• Tittlinger granite ( Tittling, Bayerischer Wald )
• Worm Mountain granite ( Harz, Lower Saxony )

Health hazards of radioactivity

In granites radionuclides such as thorium, uranium and potassium -40 are present in different amounts of highly enriched. The health hazards of exposure to radiation, emanating from granite slabs in the household or the decay products of radon, is compared to the natural background radiation or other sources of radiation, such as X-ray technology is negligible. Dr. David J. Brenner, director of the Center for Radiology Research at Columbia University in New York, estimates that the risk of cancer due to the radiation exposure from granite slabs in the household ( even if they are very highly enriched ) in the range of one in a million lies.

Other features

Special features are the " cushion-like " weathering ( Wollsackverwitterung ) and the thereby occurring under conditions favoring moss- grown surface of the further disintegration of soil-forming Grus ( fine-grained decomposition products of the rock ), the emergence of block nations, and bogs.

Landforms of this type are sometimes the subject of a tourism marketing in " mystical projects " and seminars, previous stories of witches and many loose stones in which you can measure his strength. From weathered granite rocks occur along with other kaolin and Quarzgrus. At Monte Kaolino in der Oberpfalz the " residual quartz " is piled up to an event hill. Other weathering products include clay minerals.