Serpentinite
Serpentinites are metamorphic rocks that have formed mainly from the conversion of peridotites under the action of pressure and temperatures at depth ( mantle ). The name derives from the rock are the main mineral constituents which Serpentinminerale, including chrysotile, Klinochrysotil, Orthochrysotil, Parachrysotil, lizardite or antigorite.
- 3.1 Europe
- 3.2 Africa
- 3.3 America and the Caribbean
- 3.4 Asia
- 4.1 Naturwerkstein name (selection)
Terminology
In everyday speech habits of the term occurs on serpentine. This often meant Serpentinitgesteine . Also it is used for unspecified minerals of the serpentine group. Although both meanings are causally linked, is to pay attention to the mineralogical or petrographic context in each case. Because of this nomenclatural " predicament " carries the rock described herein the term serpentinite.
Petrography
Serpentinites arise from the pressure and heat (300 to 500 ° C) induced change ( orogenic regional metamorphism ) of olivines, pyroxenes and amphiboles in peridotites ( parent rock ). Here, this process is initially along small cracks in the crystal structure of the parent rock and olivine are formed from thin Serpentinhäutchen chrysotile fibers. These fibrous crystals grow further into the surrounding grain structure it. The forming on this way network of crystal fibers creates voids that fill up again with young (smaller) chrysotile and lizardite incurred. If higher temperatures, in addition antigorite is formed. Parallel to these processes creates finely grained magnetite. In another sequence, the orthopyroxene is converted after olivine, which begins in the crystal aggregates according to a similar process with initial vein formation. The minerals clinopyroxene, anthophyllite and cummingtonite are affected by the transformation processes less and suffer them at most at a late stage of rock formation. This complex process is called serpentinization and takes place towards differentiated silicate parageneses. It may incidentally involve carbonates formed thereon and by other processes ( metasomatism ), new minerals and accompanying rocks.
As an additional process may be subject by hydrothermal processes the serpentinites of a CO2 - metasomatism. Here, calcite re-forms, which passes through the serpentinite in different ways and may contribute to the transformation of the rock in ophicalcite. Under special circumstances, the CO2 metasomatism continues until complete conversion of the serpentinite in magnesite and dolomite rocks.
Structure
The microstructure of serpentinites can be very different depending on the previous rock-forming and tectonic - metamorphic processes. The structure of images are very differentiated from deposit to deposit and causally related to their complex modes of formation. As the name of this rock group from the Latin derivation of the snake ( serpens ) points, one speaks in wavy - banded textures arising from an ophiolite structure (Greek Ophites, snake like that). Because of their sometimes showy texture serpentinites were formerly called snake stones. Tectonically highly stressed Serpentinitmassen often show a Brekzienstruktur.
Often two images:
- Ophiolithisches a structure that shows like a snake coiled ribbons or strips and umflossene, knot -like inclusions ( in the vernacular sometimes called Bänderserpentin );
- The texture of a tectonic breccia cementation of Serpentinmineralen and / or calcite, inter alia, Minerals ( partially Übergangsfazies to ophicalcite ). She is from the millimeter to decimeter typical.
Color game
The colors of Serpentinitgesteinen can be very different. General knows they are as strong green materials in different shades. Some of them are burgundy to reddish brown, and even dark brown. There are also black, black and shades of green to bright green varieties. Especially great is the color match the Zöblitzer serpentine ( Zöblitz, in the Saxon Erzgebirge). In Ligurian and Turkish varieties, it may happen that within individual Brekzientrümmer the color changes from wine red to green.
The brecciated texture can be visually deepening if the spaces between the rock debris not with similarly colored Serpentinitmassen but with calcite or other light minerals ( chlorite, magnesite, chrysotile, etc. ) are filled.
Accompanying rocks
As an accompanying rocks, due to the very complex transformations in the formation of serpentinites and subsequent mixing with contact rocks occur:
- Chlorite
- Talk rocks
- Talk - actinolite rocks
- Amphibolgesteine
Mineral composition
In addition to these main minerals found in serpentinites often magnetite or hematite in considerable amounts. The magnetite content in dark serpentinites can cause a magnet in close proximity responds noticeably to rock. If more than the above listed minerals and rocks typical occur, the rocks are, for example, referred to as garnet serpentinite or bronzite serpentinite. When chrysotile asbestos leading serpentinites is an acute danger during processing.
An associated with the metamorphosis, specific appearance of serpentinites is the occurrence of minerals in fractures. These include talc, actinolite, nephrite, Amianth, andradite and various carbonates. Some vein shaped formations of this divide minerals provide physical-mechanical weaknesses in the rock dar. This publication is for rock mechanics / engineering geological considerations and technical applications ( natural stone ) is of considerable importance.
An exhaustive statement about the complex mineral composition of all Serpentinitgesteine can not give up. The various sub-processes in their formation, subsequent conversions and reactions with contact rocks produce an almost unmanageable diversity of each mineral socialization. For this reason and the alternating structure features serpentinites are distinguished by type. The dense green Serpentinitgesteine from the border area of Italy, France and Switzerland are classified by some authors as alpinotype serpentinites.
Occurrence of Serpentinitgesteinen
In principle, serpentinites occur at the surface in areas previously significantly tectonic effects with moderate to severe degrees of metamorphism and were lifted up from a greater depth. For this reason, they are found only relatively small areas and they have compared to sedimentary rocks only a limited extent. Typical sectors are ancient subduction zones along continental plate boundaries and fracture zones and fold mountains. They are also part of the oceanic crust at mid-ocean ridges and plate boundaries.
Some selected and known occurrences are listed in the following table.
Europe
- Italy, Switzerland, Austria, Südalpenraum ( Penninic zone), the largest European Serpentinitkomplex
- France, Italy, in the western Alps; Corsica
- Italy, Liguria, Genoa and La Spezia
- Czech Republic, in Carlsbad Mountains
- Germany, in the Saxon Erzgebirge in Zöblitz ( Zöblitzer serpentine)
- Germany, in the edge region of Saxony Granulitgebirge
- Germany, in the Münchberger gneiss mass
- Croatia, in foothills of the Dinarides
- Russia, Caucasus, Urals
- Czech Republic, Moldanubicum in Altvatergebirge (small outcrops )
- Poland, in the foothills of Zobtenberges
Africa
- South Africa, as part of the Barberton Greenstone Belt
- Zimbabwe, columnar foothills of Greenstone Belt structures
- Ethiopia, along Precambrian formations
America and the Caribbean
- Cuba, along the Atlantic coast side
Asia
- Russia, flank regions of the Urals, Western Sayan, Tuva
- India, in the region of Rajasthan
- Turkey, Anatolia, represented in the unfolding alpidischen
- Georgia, in the Caucasus (small outcrops )
- Taiwan
Economic use
The types of natural stone represented in international trade are not sufficiently addressed solely under the " serpentine ". In petrographic sense, it is also about Serpentinitbrekzien and Ophicalcite.
Just the summarized under the following trade name " Verde Alpi " Natural stones have characteristics of both groups of rocks. In the Aosta Valley varieties Verde Issoire ( quarry Cret Blanc) and Verde San Denis ( quarry Blavesse ) are terminated at Châtillon. A few kilometers south we find the place of decomposition of the variety Verde Issogne ( quarry Issogne Fleurant ). All three show properties, but satisfy the type ophicalcite also a Serpentinitbrekzie. Not far from Châtillon, above the village of Verrayes exists a very large quarry on the mountain massif Aver ( Becca d'Aver ), is obtained in the underground and aboveground Serpentinitbrekzie to a significant extent (as of 2007 ). This leads the trade name Verde Aver. East of Verrayes wins another operation in the quarry Raffort a Serpentinitbrekzie under the trade names Chiesa Verde and Verde Antico. More serpentinite cut stones come from the neighboring Val di Gressoney. In Germany Serpentint - stone varieties are traded from the Aosta Valley mostly under the general name of Verde Alpi and rarely distinguished fine. Some cultivar names are not protected, other.
The naming of varieties in the international natural stone trade does not always at first sight comprehensible contexts. The variety available today Verde Guatemala comes from India and is also traded under its regional names ( see below). It is probable that the name refers to a previously activated occurrence in Guatemala with similar texture.
Natural stone name (selection)
Common natural stone names for Serpentinitgesteine are:
- Germany Zöblitzer serpentine (Saxony, Zöblitz )
- Hohenstein serpentine (Saxony, Hohenstein- Ernstthal )
- Serpentinite Wurlitz ( Upper Franconia, Wurlitz at Rehau )
- Serpentine heritage village ( Upper Palatinate, heritage village near Tirschenreuth )
- Bronzitserpentinit Kuhschnappel (Saxony, Kuhschnappel near Zwickau )
- Verde Naoussa ( Macedonia region in Naoussa and Veria )
- Verde Larissa (with Larisa )
- Tinos Green ( Island of Tinos )
- Verde Guatemala, Green actually Rajasthan ( Rajasthan )
- Rosso Levanto ( La Spezia in Liguria region )
- Verde Alpi, a collective term for numerous and significant variations following (about 15 Quarries / changing operating periods) commercial varieties (some ophicalcite ), Aosta Valley
- Verde Prato ( Tuscany Region )
- Verde Serrano (Region Pelo Malo )
- Tauern Green ( Hinterbichl near the GROßVENEDIGER )
- Hermit Serpentine (North Bohemia in Karlovy Vary)
- Rosso Levanto Turchia or Cherry Red ( province of Elazig Guleman at Altinoluk )