Antigorite
| Antigorite | |
|---|---|
 |
|
| General and classification | |
| other names |
Leaf serpentine |
| chemical formula |
|
|
Mineral class (and possibly department) |
Silicates and Germanates |
|
System no. to Strunz and to Dana |
9.ED.15 ( 8th edition : VIII / H.27) 71.01.02a.01 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic; m |
| Room group (no.) | Cm (No. 8) |
| Lattice parameters |
a = 5.42 Å ; b = 9.24 Å; c = 7.27 Å β = 91.3 ° |
| Formula units | Z = 1 |
| Physical Properties | |
| Mohs hardness | 2.5 to 3.5 |
| Density (g / cm 3 ) | measured: 2.65; calculated: 2.61 |
| Cleavage | completely according to {001}, observed according to {100} and {010} |
| Break ; Tenacity | shell-like, splintery |
| colour | white, gray, yellowish, light green to dark green, brownish |
| Line color | white to greenish white |
| transparency | translucent to opaque |
| shine | Greasy gloss, silk gloss, resin to wax gloss, earthy matt |
| Crystal optics | |
| Refractive indices |
n α = 1.555 to 1.567 n β = 1.560 to 1.573 n γ = 1.560 to 1.573 |
| Birefringence | δ = 0.005 to 0.006 |
| Optical character | biaxial negative |
| Axis angle | 2V = 20 to 50 ° |
Antigorite , also known as leaf serpentine , is a frequently occurring mineral from the serpentine group within the mineral class of "silicates and germanates". It crystallizes in the monoclinic crystal system with the idealized chemical composition of Mg 6 [(OH) 8 | Si 4 O 10 ], and is thus chemically seen a magnesium - silicate . Structurally, Antigorit belongs to the layered silicates ( phyllosilicates ).
Due to the mixed crystal formation with iron-containing serpentine minerals, the formula is also given in various sources as (Mg, Fe 2+ ) 6 [(OH) 8 | Si 4 O 10 ], whereby the elements magnesium and iron in the round brackets are each other can represent each other in the formula ( substitution , diadochie), but always in the same proportion to the other constituents of the mineral.
Antigorite is translucent to opaque and rarely develops small, tabular crystals . It is usually found in the form of leafy to fibrous mineral aggregates of light green to dark green, more rarely also white, gray, yellowish or brownish color.
Etymology and history
Antigorite was first discovered in the Valle Antigorio in the northern Italian region of Piedmont and described in 1840 by Eduard Schweizer, who named the mineral after its type of locality .
The area on the Geisspfad in the Binn valley in the Swiss canton of Valais is considered a co-type locality . Type material of the mineral is kept at the ETH Zurich in Switzerland (catalog no. Wi4868).
classification
Already in the outdated but still partially in use 8th edition of the mineral classification by Strunz of Antigorit belonged to the mineral class of "silicates and Germanates" and then to the Department of " phyllosilicates (phyllosilicates)" where he collaborated with Amesit , berthierine , Brindleyit , Carlosturanit , chrysotile , Cronstedtit , Dozyit , fraipontite , Greenalith , Karpinskit , Karyopilit , Kellyit , lizardite , népouite and Pecorait the " serpentine " with the system no. VIII / H.27 .
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also classifies the antigorite in the category of "phyllosilicates". This is, however, further subdivided according to the layer structure, so that the mineral can be found according to its composition in the sub-section "Layered silicates (phyllosilicates) with kaolinite layers, composed of tetrahedral and octahedral networks", where it can also be found together with amesite, berthierin, brindleyite, chrysotile , Cronstedtite, Fraipontite, Greenalite, Karyopilite, Kellyite, Lizardite, Manandonite, Népouite and Pecoraite the "serpentine group" with the system no. 9.ED.15 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the antigorite to the class of "silicates and Germanates" and there in the department of "layered silicate minerals". Here he is the only member of the "serpentine group" with the system no. 71.01.02a can be found in the subsection “ Layered Silicates: Layers of six-membered rings with 1: 1 layers ”.
Modifications and varieties
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The compound Mg 6 [(OH) 8 | Si 4 O 10 ] is trimorphic and, in addition to the monoclinic crystallizing antigorite, also comes as a monoclinic or orthorhombic crystallizing chrysotile ( clinochrysotile , orthochrysotile and parachrysotile ) and as a monoclinic, trigonal or hexagonal crystallizing lizardite ( lizardite- 1M , Lizardite-1T , Lizardite-6T 1 , Lizardite-2H 1 and Lizardite-2H 2 ), whereby the monoclinic modifications differ in their space group .
"Bowenite" is a light to dark apple-green variety of antigorite that occurs in coarse aggregates and the surface grain of which often appears speckled or cloudy. James Dwight Dana coined the name in 1850 in honor of George Thomas Bowen (1803-1828), a chemist, mineralogist and former professor at the University of Nashville .
“Bastite” or “Schillerspat”, on the other hand, is a pseudomorphism from Antigorite to Enstatite .
Education and Locations
Antigorite is generally metamorphically formed from serpentinite , but also from other ultrabasic rocks , where it usually occurs in paragenesis with other serpentine minerals , chromite , magnetite and / or olivine . Furthermore, antigorite can arise from hydrothermal metasomatosis in dolomite , limestone and marble .
Even if the serpentine as a whole is one of the most frequently occurring and rock-forming minerals, the mineral to be addressed as antigorite is a rather rare mineral formation, which can sometimes be abundant at different sites, but is generally not very widespread. Worldwide around 600 sites are known to date (as of 2014). In addition to its type locality Valle Antigorio and close to the municipality of Baceno in this valley , the mineral was also found in many places in the Piedmont region in Italy, such as Piasco , Cálea (municipality of Lessolo ), Rocca Canavese , Balangero and Alagna Valsesia . It was also found at various sites in the Aosta Valley and in the regions of Liguria , Lombardy , Sardinia , Trentino-South Tyrol , Tuscany and Veneto .
In Germany, Antigorit could only be found in the "Winterbauernhof" quarry near Schuttertal and on the Scheibenfelsen near the municipality of Todtmoos in Baden-Württemberg, in the "Heß" quarry near Wurlitz (Rehau), in the former graphite pit Kropfmühl , on Peterlesstein near Kupferberg and in "Heinrich" shaft near Gailbach in Bavaria; in the marble quarry “Dr. Linck “near Hochstädten (Bensheim) in Hesse; on the Backenberg near Güntersen and in a gabbro quarry in the Radau valley in Lower Saxony; in the “Kuhlenberg” quarry near Silbach in North Rhine-Westphalia; on the Arensberg near Zilsdorf in Rhineland-Palatinate and in the Zöblitz serpentine quarry, in the "Adam Heber" pit (shaft 43) near Neustädtel (Schneeberg) , in the "Diethensdorf" quarry near Chemnitz-Markersdorf , on Pfaffenberg near Waldheim , in the Kiefernberg quarry near Hohenstein -Ernstthal and in a marble quarry at Hohen Hain near Limbach-Oberfrohna in Saxony. As a rock-forming mineral , antigorite occurs in the serpentinites of the Upper Palatinate, particularly in the Erbendorf area .
In Austria, the mineral was found in the area around Friesach - Hüttenberg , the Hohe Tauern from Carinthia to Salzburg, at several sites in Styria and in the Virgen and Zillertal in Tyrol.
In Switzerland Antigorit stepped next to his co-type locality Geisspfad still moiry glacier and on the Riffelalp in the canton of Valais, at Cima Sgiu in Val Carassino in the canton of Ticino and the Cavloc Lake in Fornotal (Valley of the Fornogletschers ) in Cotschens at Lai da Marmorera and at Quadrada in the Puschlav valley in the canton of Graubünden.
Other sites include Egypt, Ethiopia, Antarctica, Argentina, Australia, Brazil, Bulgaria, China, Ecuador, Finland, France, Greece, Greenland, Indonesia, Japan, Canada, the Republic of the Congo, Cuba, Morocco, Myanmar ( Burma ), New Zealand, North Korea, Norway, Oman, Pakistan, Poland, Romania, Russia, Sweden, Zimbabwe, Slovakia, Spain, South Africa, Taiwan, Czech Republic, Hungary, the United Kingdom (UK), the United States of America ( USA) and Cyprus.
Crystal structure
Antigorite crystallizes monoclinically in the space group Cm (space group no. 8) with the lattice parameters a = 5.42 Å ; b = 9.24 Å; c = 7.27 Å and β = 91.3 ° as well as one formula unit per unit cell .
use
High-quality antigorite is used together with other serpentine minerals under the trade name "Noble serpentine" as stone in architecture and handicraft. Stones with a visually appealing texture are occasionally made into gemstones which, when they are fibrous, have a silk-like sheen .
Is known among other things, a green speckled or mottled antigorite variety, which in cabochon or as tumbled stone is marketed under the trade name "Chyta".
See also
literature
- Eduard Schweizer: About the antigorite, a new mineral. In: Annals of Physics and Chemistry. Volume 19 (1840), pp. 595-599 ( PDF 281.2 kB )
- Helmut Schrätze, Karl-Ludwig Weiner: Mineralogy. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 843-845 .
- Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 258 ( Dörfler Natur ).
Web links
- Mineral Atlas: Antigorite (Wiki)
- Webmineral - Antigorite
- Database-of-Raman-spectroscopy - Antigorite
- American-Mineralogist-Crystal-Structure-Database - Antigorite
Individual evidence
- ↑ a b c d e Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 677 .
- ^ IMA / CNMNC List of Mineral Names; January 2014 (PDF 1.5 MB)
- ↑ a b c Stefan Weiss: The large Lapis mineral directory. All minerals from A - Z and their properties . 5th completely revised and supplemented edition. Weise, Munich 2008, ISBN 978-3-921656-70-9 .
- ↑ a b c d e Antigorite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF kB )
- ↑ a b c Mindat - Antigorite
- ↑ Hans Lüschen: The names of the stones. The mineral kingdom in the mirror of language . 2nd Edition. Ott Verlag, Thun 1979, ISBN 3-7225-6265-1 , p. 318 (serpentine 2.) .
- ↑ Mindat - picture of the type material from the Geisspfad in the Binntal, which is kept in the ETH Zurich (Switzerland)
- ^ Walter Schumann: Precious stones and gemstones. All species and varieties in the world. 1600 unique pieces . 13th revised and expanded edition. BLV Verlags-GmbH., Munich et al. 2002, ISBN 3-405-16332-3 , p. 218 .
- ↑ Mindat - Number of localities for Antigorit
- ↑ B. Klinkhammer, F. Rost: The serpentinites of the Upper Palatinate Forest . In: Association of Friends of Mineralogy and Geology (Ed.): Aufschluss . Special volume 26, 1975, p. 39-64 .
- ↑ Find location list for Antigorite in the Mineralienatlas and in Mindat