Anorthite
Anorthite is a mineral from the mineral class of " silicates and Germanates ", more specifically, a framework silicate ( tectosilicate ) from the group of the feldspars, which may be abundant in various localities in part, but overall is not widespread.
Anorthite crystallizes in the triclinic crystal system with the idealized chemical composition Ca [ Al2Si2O8 ] and usually develops short prismatic crystals, but also lamellar, granular or massive mineral aggregates of white, gray or reddish color with white stroke color. The surfaces of transparent to translucent crystals have a glass-like finish.
Anorthite is a member of the plagioclase - mixed batch consisting of the minerals:
- Albite: Na [ AlSi3O8 ] (0-10% anorthite )
- ( Oligoclase ): (Na, Ca) (Si, Al) 4O8 (10-30% anorthite )
- ( Andesine ): (Na, Ca) [ (Si, Al) 4O8 ] (30-50% anorthite )
- ( Labradorite ): (Ca, Na) [ (Si, Al) 4O8 ] (50-70% anorthite )
- ( Bytownite ): (Ca, Na) [ (Si, Al) 4O8 ] (70-90 % anorthite )
- Anorthite Ca [ Al2Si2O8 ] (90-100 % anorthite )
The composition of the individual intermediate links was arbitrarily determined, as can the individual minerals differ only by chemical analysis. Therefore, only the end members albite and anorthite by the International Mineralogical Association (IMA ) are recognized as a distinct minerals.
Etymology and history
Was first discovered anorthite at Monte Somma in Italy and described in 1823 by Gustav Rose, who ἀν the mineral after the Greek word - as a negation of ὀρθός orthos for " right", ie composed " unsustainable " or "not ( to ) properly " named in reference to the oblique form of the triclinic Anorthitkristalle.
Classification
In the now outdated but still in use 8th edition of the mineral classification by Strunz the anorthite belonged to the mineral class of " silicates and Germanates " and then to the Department of " framework silicates ( tectosilicates ) " where he together with the recognized minerals albite, anorthoclase, Banalsite, Dmisteinbergit, Filatovit, oligoclase, Stronalsit and Svyatoslavit and the intermediate members andesine, labradorite and Bytownite the independent feldspar subset of " anorthoclase anorthite Banalsite series" was formed.
The valid since 2001 and used by the IMA 9th edition of the Strunz'schen Mineral classification assigns the anorthite also in the class of " silicates and Germanates " there, however, in the new department of " framework silicates ( tectosilicates ) without zeolitic H2O" one. This department is also further divided according to the possible presence of other anions, so that the mineral is found according to its composition in the subsection " framework silicates ( tectosilicates ) without additional anions ", where the together with the recognized minerals albite, Ling Unit and Reedmergnerit and pontics andesine, Bytownite, labradorite and oligoclase the " plagioclase - group " with the system no. 9.FA.35 forms.
The mainly common in English-speaking classification of minerals according to Dana assigns the anorthite in the class of " silicates and Germanates " and then in the Department of: a " framework silicates Al- Si lattice ". Here he is with the " plagioclase series" with the system no. 76.01.03 found within the subdivision " framework silicates with Al- Si lattice ".
Education and Locations
Anorthite is either formed in magmatic gabbro, basalt and anorthosite or in metamorphic rocks. The rock anorthosite which forms significant parts of the lunar crust, consists almost entirely of anorthite.
Overall, anorthite so far (as of 2011) detected at 700 localities. Apart from its type locality Monte Somma, the mineral in Italy was still also located in Campania Vesuvius, found at Osilo in the Sardinian province of Sassari in Spoleto in Umbria, as well as at several locations in the regions of Lazio, Lombardy, Piedmont, Sicily, Trentino -Alto Adige and Tuscany.
Noteworthy due to excellent crystal finds is also the island of Miyake- jima in the Japanese prefecture of Tokyo, were found on the Anorthitkristalle with up to 5 cm in diameter.
In Germany, the mineral is found among others in Schollach ( Eisenbach ) in Baden- Württemberg; Maroldsweisach, Roehrnbach and Wiesau in Bavaria; Eschwege, casting and Hanau in Hesse; in Bad Harzburg in Lower Saxony; several places in the Eifel area in Rhineland -Palatinate; at Chemnitz and Schneeberg in Saxony; at Plön in Schleswig -Holstein; and in Gera and Schmalkalden in Thuringia.
In Austria anorthite appeared primarily in Carinthia, Lower Austria and Styria, and in Switzerland, he found himself so far only in Vicosoprano in the canton of Graubünden and Ticino.
Other localities are Algeria, Angola, Mount Erebus in Antarctica, Australia, Bolivia, Brazil, Chile, China, Costa Rica, El Salvador, Finland, France and the French West Indies island of Guadeloupe, Greece, Greenland, India, Indonesia, Ireland, Israel, Japan, Cameroon, Canada, Kyrgyzstan, South and North Korea, Libya, Madagascar, Mexico, Morocco, Namibia, New Zealand, Norway, Oman, Pakistan, Palestine, Papua New Guinea, Paraguay, Peru, Poland, Portugal, Republic of Congo, Romania, Russia, Sweden, Slovakia, Spain, St. Kitts and Nevis, Saint Lucia, South Africa, Tanzania, the Czech Republic, Turkey, Ukraine, Hungary, the United Kingdom ( UK), the United States of America ( USA) and the Central African Republic.
Even in rock samples of the Mid-Atlantic Ridge and the East Pacific Rise and outside the earth beside the moon still in the tail of comet Wild 2 material anorthite could be detected.
Crystal structure
Anorthot crystallized in the triclinic space group ( Raumgruppen-Nr. 2) with the lattice parameters a = 8.18 Å; b = 12.88 Å; c = 14.17 Å; α = 93.2 °; β = 115.8 ° and γ = 91.2 ° and 8 formula units per unit cell.