Bytownite

from Wikipedia, the free encyclopedia
Bytownite
Bytownite-mrz296a.jpg
Bytownite from the Dorado Mine, Casas Grandes , Mexico (size: 3.7 cm × 2 cm × 1.3 cm)
General and classification
chemical formula (Ca, Na) [(Si, Al) 4 O 8 ]
Mineral class
(and possibly department) 		Silicates and Germanates - framework silicates
System no. to Strunz
and to Dana 		9.FA.35 ( 8th edition : VIII / J.07)
76.01.03.05
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Room group (no.) I 1 (No. 2)
Lattice parameters a  = 8.19  Å ; b  = 12.88 Å; c  = 14.20 Å,
α  = 93.4 °; β  = 116.0 °; γ  = 90.9 °
Formula units Z  = 8
Physical Properties
Mohs hardness 6 to 6.5
Density (g / cm 3 ) measured: 2.72 to 2.74; calculated: 2.713 to 2.726
Cleavage perfect after {001}, good after {010}, indistinct after {110}
Break ; Tenacity uneven to shell-like; brittle
colour colorless, gray, white, yellow to golden yellow
Line color White
transparency transparent to translucent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.563 to 1.572
n β  = 1.568 to 1.578
n γ  = 1.573 to 1.583
Birefringence δ = 0.010 to 0.011
Optical character alternating biaxially
Axis angle 2V = measured: 86 °, calculated: 80 ° to 88 °
Pleochroism colorless

Bytownite , like andesine , oligoclase and labradorite, is no longer considered an independent mineral , but is a rather seldom occurring intermediate link from the mixed series of plagioclase with the end links albite and anorthite from the group of feldspars within the mineral class of silicates . Its anorthite content is by definition 70 to 90% (An 70-90 ).

Bytownite crystallizes in the triclinic crystal system with the general chemical composition (Ca, Na) [(Si, Al) 4 O 8 ]. The elements calcium and sodium or silicon and aluminum indicated in the round brackets can represent each other in the formula ( substitution , diadochy), but are always in the same proportion to the other components of the mineral. Structurally, Bytownite belongs to the scaffold silicates .

In nature, Bytownite is mostly found in the form of fissile masses or irregular grains, but also develops tabular to short prismatic crystals and twins according to the Albite, Carlsbad and Periclin laws. Unharmed crystal surfaces have a glass-like sheen , whereas cleavage surfaces have a more mother-of-pearl shimmer . In its pure form, Bytownite is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline training, it can also appear white and, due to foreign admixtures, take on a gray or light yellow to golden yellow color, the transparency decreasing accordingly.

Etymology and history

Bytownite was first discovered near Bytown (today Ottawa ) in the Canadian province of Ontario and described in 1836 by Thomas Thomson , who named the mineral after its type locality .

Varieties and modifications

Maskelynite is a former bytownite that originates from meteorites and has melted into glass .

Education and Locations

Golden yellow irregular bytownite crystal from the Dorado Mine, Mexico (size: 2.5 cm × 1.9 cm)

Bytownite occurs as a rock-forming mineral in the group of anorthosites . To date, a total of around 120 sites are known (as of 2014) where albite-anorthite mixed crystals with the composition of bytownite were found.

In Germany, the mineral is so far only known from Bopfingen on the western edge of the Nördlinger Ries in Baden-Württemberg, from the "Attenberg" quarry near Großen-Buseck in Hesse, from a gabbro quarry in the Radau Valley near Bad Harzburg in Lower Saxony and from the "Caspar" quarry on the Ettringer Bellerberg near Ettringen in the Rhineland-Palatinate Vulkaneifel.

In Austria they found Bytownit among others in the hut Erzberg and the nearby Wastl digging in the valley of Mosinzbaches and in Bad Eisenkappel in Carinthia, on Mitterbach digging at Gansbach (municipality Dunkelsteinerwald) and a amphibolite - disruption in Senftenberg in Lower Austria and in a basalt - quarry at Weitendorf and the "Hartner" quarry near Schwanberg in Styria.

The only known site in Switzerland so far is Piz Lizun near Löbbia ( Vicosoprano ) in the canton of Graubünden .

Other locations are in Algeria, Angola, Antarctica, Australia, China, Costa Rica, El Salvador, Finland, France, Greece, Guadeloupe, India, Italy, Japan, Canada, Madagascar, Mexico, Norway, Portugal, Russia, Sweden, Slovakia, Spain, South Korea, Tanzania, the Czech Republic, near Warkowytschi in the Ukrainian Rivne Oblast , on the US Virgin Island of Saint Thomas and in various states of the USA and in the United Kingdom (England, Scotland).

Also in rock samples from the East Pacific Ridge (EPR 12 ° 50 'N) albite-anorthite mixed crystals of the variety bytownite and labradorite could be detected.

Crystal structure

Bytownite crystallizes triclinically in space group I 1 (space group no. 2) with the lattice parameters a  = 8.19  Å ; b  = 12.88 Å; c  = 14.20 Å; α = 93.4 °; β = 116.0 ° and γ = 90.9 ° as well as 8 formula units per unit cell .

use

Colorless and yellow bytownites are coveted gemstones .

Bytownite from the USA

See also

literature

Web links

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

Individual evidence

  1. ↑ 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.  695 .
  2. ↑ a b Bytownite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 85.5 kB )
  3. ↑ a b c Mindat - Bytownite
  4. ↑ Wolfhard Wimmenauer: Petrography of igneous and metamorphic rocks . Enke, Stuttgart 1985, ISBN 3-432-94671-6 , pp. 87 .
  5. ↑ Mindat - Number of localities for Bytownite
  6. ↑ Arnd Peschel: Natural stones . 2nd Edition. Deutscher Verlag der Grundstofftindustrie, Leipzig 1983, p. 211 .
  7. ↑ List of localities for Bytownite in the Mineralienatlas and Mindat
  8. ↑ Mindat - type locality EPR 12 ° 50 'N, East Pacific Rise, Pacific Ocean