Anorthite

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Anorthite
Anorthit Miyake, Japan.JPG
Anorthite
General and classification
chemical formula CaAl 2 Si 2 O 8
Mineral class
(and possibly department)
Silicates and germanates - framework silicate, feldspar
System no. to Strunz
and to Dana
9.FA.35 ( 8th edition : VIII / J.07)
76.01.03.06
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group P 1 (No. 2)Template: room group / 2
Lattice parameters a  = 8.18  Å ; b  = 12.88 Å; c  = 14.17 Å
α  = 93.2 °; β  = 115.8 °; γ  = 91.2 °
Formula units Z  = 8
Twinning mostly twinned according to the Albit law
Physical Properties
Mohs hardness 6 to 6.5
Density (g / cm 3 ) measured: 2.74 to 2.76; calculated: 2.760
Cleavage perfect after {001}, indistinct after {010}, imperfect after {110}
Break ; Tenacity uneven to scalloped, brittle
colour gray, green, red
Line color White
transparency transparent to translucent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.573 to 1.577
n β  = 1.580 to 1.585
n γ  = 1.585 to 1.590
Birefringence δ = 0.012 to 0.013
Optical character biaxial negative
Pleochroism colorless

Anorthite is a mineral from the mineral class of " silicates and Germanates ", specifically a framework silicate (tectosilicate) from the group of feldspars is that can be abundant in various localities in part, but overall not widespread.

Anorthite crystallizes in the triclinic crystal system with the idealized chemical composition Ca [Al 2 Si 2 O 8 ] and mostly develops short prismatic crystals , but also lamellar, granular or massive mineral aggregates of white, gray or reddish color with white streak color . The surfaces of the transparent to translucent crystals have a glass-like sheen .

Anorthite is a member of the plagioclase - mixed batch consisting of the minerals:

  • Albite : Na [AlSi 3 O 8 ] (0-10% anorthite)
  • ( Oligoclase ): (Na, Ca) (Si, Al) 4 O 8 (10–30% anorthite)
  • ( Andesine ): (Na, Ca) [(Si, Al) 4 O 8 ] (30–50% anorthite)
  • ( Labradorite ): (Ca, Na) [(Si, Al) 4 O 8 ] (50–70% anorthite)
  • ( Bytownite ): (Ca, Na) [(Si, Al) 4 O 8 ] (70–90% anorthite)
  • Anorthite : Ca [Al 2 Si 2 O 8 ] (90–100% anorthite)

The composition of the individual intermediate links was determined arbitrarily, since the individual minerals can only be distinguished by chemical analysis. Therefore, only the end links albite and anorthite are recognized as independent minerals by the International Mineralogical Association (IMA).

Etymology and history

Anorthite was discovered for the first time on Monte Somma in Italy and described in 1823 by Gustav Rose , who named the mineral after the Greek word ν an- as a negation of ὀρθός orthos for "correct", thus composed "not upright" or "not (up) correct" named after the oblique shape of the triclinic anorthite crystals.

classification

In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of 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 , Dmisteinbergite , Filatovite , Oligoclase , Stronalsite and Svyatoslavit as well as the intermediate links Andesine , Bytownite and Labradorite formed the independent feldspar subgroup of the "anorthoclase-anorthite-banalsite series".

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the IMA, also assigns anorthite to the class of "silicates and germanates", but in the new section of "tectosilicates without zeolitic H 2 O" . This section is further subdivided according to the possible presence of further anions , so that the mineral can be found according to its composition in the sub-section “Tectosilicates without additional anions”, where it can be found together with the recognized minerals albite, lingunite and reed mergnerite as well as the Intermediate members andesine, bytownite, labradorite and oligoclase are the "plagioclase group" with system no. 9.FA.35 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns anorthite to the class of "silicates and germanates" and there in the department of "framework silicates: Al-Si lattice". Here it is together with in the "plagioclase series" with the system no. 76.01.03 to be found in the sub-section “ Framework silicates with Al-Si lattice ”.

Crystal structure

Anorthite crystallizes triclinically in the space group P 1 (space group no. 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 . Template: room group / 2

Education and Locations

White anorthite crystals, grown in the volcanic ejection of Monte Somma, Italy (size: 6.9 × 4.1 × 3.8 cm)

Anorthite forms either igneously in gabbro , basalt and anorthosite or in metamorphic rocks. The rock anorthosite, which forms significant parts of the lunar crust , consists practically entirely of anorthite.

Under extremely high pressure of ~ 29 GPa (~ 290 kBar), as can occur during impact metamorphosis as a result of a meteorite impact , anorthite-rich plagioclase is converted to maskelynite , a diaplectic glass . When the pressure is reduced, at 6–8 GPa and 1350–1000 ° C, maskelyite can crystallize to tissueintite , a pyroxene with the composition of anorthite, which has vacancies in a lattice position.

In total, anorthite has been detected at around 700 sites so far (as of 2011). Besides its type locality Monte Somma mineral in Italy was still also located in Campania Vesuvius in Osilo in the Sardinian province of Sassari , at Spoleto in Umbria and in several places of the Regions Lazio , Lombardy , Piedmont , Sicily , Trentino-Alto Adige and Tuscany found .

The island of Miyake-jima in the Japanese prefecture of Tokyo, where anorthite crystals with a diameter of up to 5 cm have been found, is also worth mentioning due to the excellent crystal finds.

In Germany the mineral was found, among other places, near Schollach (Eisenbach) in Baden-Württemberg; Maroldsweisach , Röhrnbach and Wiesau in Bavaria; Eschwege , Giessen and Hanau in Hessen; near Bad Harzburg in Lower Saxony; in several places in the Eifel in Rhineland-Palatinate; near Chemnitz and Schneeberg in Saxony; near Plön in Schleswig-Holstein; as well as at Gera and Schmalkalden in Thuringia.

In Austria, anorthite appeared mainly in Carinthia , Lower Austria and Styria and in Switzerland it was only found in Vicosoprano in the canton of Graubünden and Ticino .

Other locations are Algeria , Angola , Mount Erebus in the Antarctic, Australia , Bolivia , Brazil , Chile , China , Costa Rica , El Salvador , Finland , France and the French Antilles island of Guadeloupe , Greece , Greenland , India , Indonesia , Ireland , Israel , Japan , Cameroon , Canada , Kyrgyzstan , North and South Korea , Libya , Madagascar , Morocco , Mexico , Namibia , New Zealand , Norway , Oman , Pakistan , Palestine , Papua New Guinea , Paraguay , Peru , Poland , Portugal , the Republic of the Congo , Romania , Russia , Sweden , Slovakia , Spain , St. Kitts and Nevis , St. Lucia , South Africa , Tanzania , Czech Republic , Turkey , Ukraine , Hungary , United Kingdom (Great Britain), United States of America (USA) and the Central African Republic .

Anorthite could also be detected in rock samples from the Mid-Atlantic Ridge and the East Pacific Ridge as well as outside of the earth next to the moon and in the tail material of the comet Wild 2 .

See also

literature

Web links

Commons : Anorthite  - collection of images, videos and audio files
Wiktionary: Anorthite  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. Webmineral - Anorthite (English)
  2. a b c d e f g 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.  695 .
  3. a b c d e Mindat - Anorthite (English)
  4. a b IMA / CNMNC List of Mineral Names (English, PDF 1.8 MB)
  5. Gustav Rose : About the feldspar, albite, labrador and anorthite . In: Annalen der Physik , Volume 73, Issue 2, pages 173–208, 1823, doi : 10.1002 / andp.18230730208 .
  6. MJ Rucksack, ML Whitaker, TD Glotch, and JB Parise: Tissintite: An Experimental Investigation into an Impact-Induced, Defective Clinopyroxene. In: Acta Crystallographica . A73, 2017, p. 245 ( iucr.org [PDF; 593 kB ; accessed on January 16, 2019]).
  7. Melinda J. Rucksack, Matthew L. Whitaker, Timothy D. Glotch, John B. Parise, Steven J. Jaret, Tristan Catalano, and M. Darby Dyar: Making tissintite: Mimicking meteorites in the multi-anvil . In: American Mineralogist . tape 103 , 2018, p. 1516–1519 ( sunysb.edu [PDF; 1.1 MB ; accessed on January 16, 2019]).
  8. ^ Petr Korbel, Milan Novák: Mineral Encyclopedia . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 266 .
  9. Find location list for anorthite in the Mineralienatlas and Mindat