Serpentine group

The serpentine group ( Orphit, snake stone) refers to a group in the monoclinic crystal system crystallizing silicate minerals with the chemical composition (Mg, Fe, Ni) 6Si4O10 (OH ) 8 In brackets atoms can be represented in any combination, but always stand in the same relation to the other groups of atoms. Serpentine has a relatively low hardness of 2.5 to 4, a mostly olive-green, but occasionally yellow, brown, red, gray, black or white color and a white stroke color.

The serpentine is one of the trioctahedral layer silicates.

History

Serpentine bears his from the Latin serpens: "snake" derived probably named because of the characteristic, snake-like drawing of the mineral.

Individual minerals and varieties

According to the classification of minerals according to Strunz ( 9th edition ) following minerals belong to the serpentine group:

• Amesite Mg2Al ( AlSiO5 ) (OH) 4
• Antigorite Mg3Si2O5 (OH) 4
• Berthierine ( Fe2 , Fe3 , Al ) 3 ( Si, Al) 2o5 (OH) 4
• Brindleyit (Ni, Al) 3 (Si, Al) 2o5 (OH) 4
• Chrysotile Mg3Si2O5 (OH) 4 Klinochrysotil
• Orthochrysotil
• Parachrysotil

Various group members with each other form a mixed crystal series. The end members of the mixing series are therefore highlighted in bold. Formerly counted for serpentine Carlosturanit were also ( (Mg, Fe 2 , Ti) 21 (Si, Al) 12O28 (OH ) 34 · H2O), Dozyit ( Mg7Al2 ( Si4Al2 ) O15 (OH ) 12) and Karpinskit ( (Mg, Ni) 2Si2O5 (OH) 2).

Contrast bastit is a pseudomorph after enstatite from serpentine.

Serpentine can be as silky, asbestos -like fibers ( chrysotile ), solid as a splintery material ( chrysotile ) or with leafy habit ( lizardite, antigorite, amesite, berthierine, Odinit ) occur.

Education and Locations

Serpentine minerals are secondary and arise in converting magnesium- rich olivine in peridotite orthopyroxenes or. They are the main constituent of metamorphic rock serpentinite. Most plutonic rocks are converted into subduction zones to serpentinites. In some cases you can still recognize former structures of the original rocks. Serpentinminerale also arise in processes low-grade metamorphism ( in the greenschist facies ) or hydrothermal metasomatism ( on the ocean floor in olivinhaltigen volcanics ) by the action of water on olivine.

Locations of Serpentinitgesteinen include heritage village in Bavaria and in Zöblitz and in Hohenstein- Ernstthal in Saxony in Germany; in the Alpes- de -Haute -Provence in France; in the Aosta Valley, in Sondrio and Val Polcevera, in Liguria and in Prato in Italy; East Tyrol, in Bernstein in Burgenland, close Oppenberg in Styria and in the middle Enns in Austria; the South Urals in Russia; in the Swiss cantons of Grisons, Uri and Wallis; as well as in many regions of the United States.

From ancient importance is the occurrence in Larisa, Greece. Smaller mineable deposits are found in Britain, Croatia, Spain, Poland, Czech Republic. Important non-European deposits are located in China, Guatemala and India, South Africa, Taiwan, Turkey and Zimbabwe.

Structure

The crystal structure of the Serpentine linked as well as those of kaolinite tetrahedral layer with one octahedron. The tetrahedral sheet consists of polymerized tetrahedrons are basal oxygen atoms linked to one another and either with silicon ( lizardite, antigorite, chrysotile ), or silicon and aluminum ( amesite, berthierine, Odinit ) are occupied. The octahedral layer consists of edge-sharing octahedra with both magnesium ( lizardite, antigorite, chrysotile, amesite ) and iron ( berthierine, Odinit ) may be occupied. These, consisting of tetrahedral and octahedral structure is known as a 1:1 layer packet.

Some Serpentine are only looking flaky, on closer examination, they consist of waves with a wavelength of about 3 to 10 nanometers; these structures are also referred to as a modulated structures. Differences in morphology result from the adaptation of the narrow tetrahedral layer in the case of chrysotile and the larger octahedral layer in the case of antigorite ago. In these two varieties of the tetrahedra are tilted slightly so that the peak oxygen atoms move away from each other and so adjust the oxygen atoms of the octahedron.

Use

The massive pieces of Serpentinitgesteinen be processed until today in architecture and craftsmanship. They can be cut into mountain moist condition, cut and turned, in a dry and highly polished; Therefore you made ​​of them vessels, equipment (formerly insulators ), table tops, cladding panels, grave stones and architectural elements.

The mineral group garnierite is a component of nickel ores and is mined for the extraction of this metal particularly in New Caledonia.

Chrysotile ( one of asbestos ) was used until the 1990s mixed with cement in the construction industry, as this material is highly flame resistant and chemically inert. Later it turned out that chrysotile as the related crocidolite in its fibrous form is a hazardous material, as replacing the fine individual fibers and easily inhaled lung ( asbestosis ) and mesothelioma can trigger.

Historical use in architecture and crafts

Since the mid-16th century, gained in Zöblitz serpentine for architectural elements, such as was turned wooden balusters and polished cassette fields used. The similarity with veined marble types and the slight polishing ability contributed to the popularity of the mineral. Also, the ability has been attributed to him, it could make toxins harmless or show by cracking, which may have encouraged the production of cups and trophies made ​​of this material. In the 17th and 18th century works were provided with special gold-plated Silbermontierungen (examples in the Green Vault, Dresden), others mounted with Zinnfassungen. Architects used serpentine in the facilities of the Dresden Hofkirche ( 1739-55 ) or the Semper Opera House ( 1871-78 ). See also a more detailed description at: Zöblitzer serpentine

Safety

The fibrous chrysotile asbestos is a carcinogenic material. The other non- fibrous Serpentinvarietäten apply, however, to be harmless. When editing, however, consistently measures to protect against the inhalation of dusts are to be taken, otherwise also there silicosis or lung cancer can be triggered.