Anorthoclase

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Anorthoclase
Anorthoclase-tn23a.jpg
Anorthoklas from Kinki , Japan
General and classification
chemical formula (Na, K) AlSi 3 O 8
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.FA.30 ( 8th edition : VIII / J.07)
76.01.01.06
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol 1
Space group C 1 (No. 2, position 3)Template: room group / 2.3
Lattice parameters a  = 8.287  Å ; b  = 12.972 Å; c  = 7.156 Å,
α  = 91.05 °; β  = 116.26 °; γ  = 90.15 °
Formula units Z  = 4
Physical Properties
Mohs hardness 6th
Density (g / cm 3 ) measured: 2.57 to 2.60; calculated: 2.57
Cleavage perfect on {001}, partly on {010}, partly on {100}, {110}, { 1 10} and { 2 01}
Break ; Tenacity uneven
colour colorless, partly white, light creamy yellow, red, green
Line color White
transparency transparent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.524 to 1.526
n β  = 1.529 to 1.532
n γ  = 1.530 to 1.534
Optical character biaxial negative
Axis angle 2V = 42 ° to 52 °

Nowadays, anorthoclase is no longer considered an independent mineral , but is an alkali feldspar , a mixture of albite and orthoclase . He is - if it is classified - in the mineral class of the silicates and Germanates classified. It crystallizes in the triclinic crystal system with the chemical composition (Na, K) AlSi 3 O 8 . The composition of albite and orthoclase is given between Ab 20 Or 80 and Ab 30 Or 70 .

Anorthoclase forms short, prismatic crystals , sometimes also tabular, rhombic or flat [010]. The crystals are up to 5 cm in size.

Etymology and history

Anorthoklas was named in 1885 by Karl Harry Ferdinand Rosenbusch after the Greek for “crooked” and “break”, referring to the fact that anorthoclase has no cleavage .

classification

As a non-independent mineral, anorthoclase is usually not classified independently, but rather according to its components albite and orthoclase.

Crystal structure

Anorthoclase crystallizes triclinic in space group C 1 (space group no. 2, position 3) with the lattice parameters a  = 8.287  Å , b  = 12.972 Å, c  = 7.156 Å, α  = 91.05 °, β  = 116.26 ° and γ  = 90.15 ° and four formula units per unit cell . Template: room group / 2.3

The crystal structure of anorthoclase changes at high temperatures. The limit temperature is 388-400  ° C . Anorthoclase now crystallizes in the monoclinic crystal system in the space group C 2 / m (space group no. 12) . The lattice parameters increase slightly with increasing temperature; at 750 ° C they are a  = 8.321  Å , b  = 12.969 Å, c  = 7.148 Å and β  = 116.05 °. Due to the symmetry in the monoclinic crystal system, the angles α and γ are 90 °. Template: room group / 12

properties

Anorthoclase is very soluble in hydrofluoric acid (HF), but less soluble in hydrochloric acid (HCl).

Education and Locations

Anorthoclase is mainly formed at high temperatures in volcanic and magma rocks .

184 sites are known of Anorthoklas.

The type locality of the mineral is on the island of Pantelleria in the Free Municipal Consortium Trapani in Italy .

Nine sites have been found in Germany . In North Rhine-Westphalia there is a site in the Siebengebirge near Königswinter . In Rhineland-Palatinate , most sites are, they all lie in the Eifel . There is one site near Gerolstein and six sites at Laacher See (near Kruft , Mendig and Niederzissen ). Finally there is a site in Schleswig-Holstein in Lübeck , district Travemünde .

There are three sites in Austria . The first is in Burgenland near Oberpullendorf in Kobersdorf on the Pauliberg volcano . Another find is in the province of Carinthia in the Koralpe mountain range in the Waldenstein part of Wolfsberg . The last Austrian site is in the province of Styria , also in the Koralpe mountain range and there in the village of Schwanberg .

Other sites are in Algeria , Angola , Antarctica , Argentina , Ethiopia , Australia , Brazil , China , Eritrea , France , Greece , Honduras , Italy , Japan , Canada , Kazakhstan , Libya , Mexico , New Zealand , North Korea , Norway , Peru , Portugal , Russia , Rwanda , Sweden , Slovakia , Spain , South Africa , South Korea , Tanzania , Czech Republic , Turkey , Hungary , the United Kingdom and the United States of America .

See also

literature

  • ED Mountain: Potash oligoclase from Mt. Erebus, Antarctica and anorthoclase from Mt. Kenya, East Africa. In: Mineralogical Magazin , Volume 29, 1925, pp. 331-345
  • Eugene L. Bonduette, Arthur B. Ford: Physical properties of anorthoclase from antarctica. In: American Mineralogist , Volume 51, 1966, pp. 1374–1387 ( PDF )
  • R. de Pieri, S. Quareni: The crystal structure of an anorthoclase: an intermadiate feldspare. In: Acta Crystallographica , Vol. 29, 1973, pp. 1483-1487

Web links

Commons : Anorthoclase  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b The numbering of this axis position does not correspond to the order of the International Tables for Crystallography , because it is not listed there.
  2. ↑ a b c d e f g Anorthoclase , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 59, 7 kB )
  3. ^ ISE Carmichael, WS MacKenzie: The lattice parameters of high-temperature triclinic sodic feldspars. In: Mineralogical Magazine , Vol. 33, 1964, pp. 949–962 ( PDF )
  4. ↑ a b c d e f Anorthoclase near Mindat (English)
  5. ↑ George E. Harlow: The anorthoclase structure: the effects of temperature and composition. In: American Mineralogist , Volume 67, 1982, pp. 975–996 ( PDF )
  6. ↑ Mineral Atlas: Anorthoclase