Bytownite
Bytownite applies as andesine, oligoclase and labradorite no longer as a separate mineral, but is a rarely occurring intermediate member from the mixed batch of plagioclase with the end members albite and anorthite from the group of the feldspars within the mineral class of silicates. Anorthite is defined to be 70 to 90% ( An70 -90).
Bytownite crystallized in the triclinic crystal system having the general chemical composition (Ca, Na) [ (Si, Al) 4O8 ]. The values given in the parentheses of the elements calcium and sodium or silicon and aluminum can in the formula each represent each other (substitution, Diadochie ), but are always in the same proportions to the other components of the mineral. Structurally Bytownite belongs to the framework silicates.
In nature, Bytownite is usually in the form of cleavable masses or irregular grains, but also develops tabular to short prismatic crystals and twins after albite, Carlsbad, and pericline law. Uninjured crystal faces have a glass-like luster, cleavage surfaces shimmer on the other hand rather nacreous. In its pure form Bytownite is colorless and transparent. But it can also appear white and accept by foreign admixtures a gray or pale yellow to golden yellow color by multiple refraction due to lattice defects or polycrystalline training, the transparency decreases accordingly.
Etymology and history
Was first discovered Bytownite near Bytown (now 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
Maskelynit is a native of meteorites to molten glass, a former Bytownite.
Education and Locations
Bytownite occurs as a rock forming mineral in the group of anorthosites. In total there are around 120 localities known so far (as of 2014), in which albite - anorthite crystals were mixed with the composition of Bytownite found.
In Germany, you know the mineral so far only from Bopfingen on the western edge of the Nordlinger Ries in Baden- Württemberg, the quarry " Attenberg " at Great -Buseck Hessen, from a gabbro quarry in Radautal in Bad Harzburg in Lower Saxony and from the quarry " Caspar " on Ettringer Bellerberg at Ettringen in the Rhineland-Palatinate Eifel.
In Austria they found Bytownite among others at Hüttenberger Erzberg and the nearby Wastl ditch in the valley of Mosinzbaches and in Bad Eisenkappel in Carinthia, on Mitter Bachgraben at Gansbach (municipality Dunkelsteinerwald ) and at a amphibolite digestion at Senftenberg in Lower Austria as well as in a basalt quarry near Wide village and the quarry " Hartner " in swan mountain in Styria.
The only known locality in Switzerland Piz Lizun at Löbbia (municipality Vicosoprano ) in the canton of Grisons.
Other localities lie 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, Czech Republic, at Warkowitschi ( Варковичі ) Rivne Oblast of Ukraine, on the U.S. Virgin Islands Saint Thomas and in various states across the United States and the United Kingdom (England, Scotland).
Even in rock samples from the East Pacific Rise (EPR 12 ° 50 ' N) albite - anorthite solid solution in the variety Bytownite and labradorite could be detected.
Crystal structure
Bytownite crystallized in the triclinic space group I1 ( Raumgruppen-Nr. 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 ° and 8 formula units per unit cell.
Use
Colorless and yellow Bytownite are coveted gemstones.