Osumilith

from Wikipedia, the free encyclopedia
Osumilith
Osumilite - Ochtendung, Eifel, Germany.jpg
Rare combination of Osumilite grown side by side in tabular and prismatic habit (image size: 1.5 mm)
Location: tub heads, Ochtendung, Eifel, Germany
General and classification
chemical formula KFe 2 (Al 5 Si 10 ) O 30
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.CM.05 ( 8th edition : VIII / E.22)
63.02.01a.06
Similar minerals Cordierite
Crystallographic Data
Crystal system hexagonal
Crystal class ; symbol dihexagonal-dipyramidal; 6 / m  2 / m  2 / m
Space group P 6 / mcc (No. 192)Template: room group / 192
Lattice parameters a  = 10.09  Å ; c  = 14.33 Å
Formula units Z  = 2
Physical Properties
Mohs hardness 5 to 6
Density (g / cm 3 ) measured: 2.58 to 2.68; calculated: 2.71
Cleavage indistinctly parallel and at right angles to {0001}
Break ; Tenacity brittle
colour dark blue, dark gray, green, brown, black
Line color Please complete!
transparency transparent to translucent
shine Glass gloss
Crystal optics
Refractive indices n ω  = 1.539 to 1.547
n ε  = 1.545 to 1.551
Birefringence δ = 0.0040
Optical character uniaxial alternating
Axis angle 2V = 28 to 45 °
Pleochroism strong: ω = light blue to blue-violet, pale pink, pale yellowish brown; ε = colorless to brown

Osumilith is a rarely occurring mineral from the mineral class of " silicates and germanates ". It crystallizes in the hexagonal crystal system with the idealized composition KFe 2 (Al 5 Si 10 ) O 30 , so from a chemical point of view it is a potassium - iron- silicate, which structurally belongs to the ring silicates .

Osumilith mostly develops transparent to translucent crystals with a tabular to prismatic habit of up to five millimeters in size, but can also be found grown in or grown in massive aggregates . The predominantly dark blue to dark gray, more rarely green, brown or black crystals have a glass-like sheen .

Etymology and history

Osumilith was first found in 1956 near Sakkabira on the Ōsumi Peninsula in Japan and described by Akiho Miyashiro , who named the mineral after its type of locality .

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the osumilite belonged to the general division of " ring silicates (cyclosilicates)", where together with milarite it forms the " milarite-osumilite group " with the system no. VIII / E.22 and the other members Almarudit , Armenit , Berezanskit , Brannockit , Chayesit , Darapiosit , Dusmatovit , Eifelit , Emeleusit , Faizievit , Poudretteit , Merrihueit , Oftedalit , Osumilith- (Mg) , Roedderit , Shibkovit , Sogdianit , Sugilith , Trattnerit , Yagiit and Yakovenchukit- (Y) made.

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also classifies Osumilith in the category of "ring silicates (cyclosilicates)". This is, however, further subdivided according to the type of ring structure, so that the mineral can be found according to its composition in the subdivision "[Si 6 O 18 ] 12− - six-double rings", where it is found together with almarudite, armenite, berezanskite, brannockite , Chayesit, Darapiosit, Dusmatovit, Eifelit, Friedrichbeckeit , Merrihueit, Milarit, Oftedalit, Osumilith- (Mg) , Poudretteit, Roedderit, Shibkovit, Sogdianit, Sugilite, Trattnerit and Yagiit form the unnamed group 9.CM.05 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Osumilith to the class of "silicates and germanates", but there in the more finely divided division of "ring silicates: condensed rings". Here it is in the " Milarite Osumilith Group (Milarite Osumilith Subgroup) " with the system no. 63.02.01a can be found in the subsection “ Ring Silicates : Condensed, 6-membered Rings”.

Crystal structure

Osumilith crystallizes hexagonally in the space group P 6 / mcc (space group no. 192) with the lattice parameters a  = 10.09  Å and c  = 14.33 Å as well as two formula units per unit cell . Template: room group / 192

properties

Osumilith is strongly dichroistic , so it shows two different colors when light passes through from two different directions. Continuous light in the direction of the main optical axis makes the Osumilith appear light blue to blue-violet, pale pink or pale yellowish-brown. Perpendicular to this it is colorless or brown.

Education and Locations

Thick tabular Osumilite with mullite from tub heads, Ochtendung, Eifel
Image size: 1.5 mm

Osumilith forms in metamorphic granulite facies (MP / HT) at temperatures around 1000 ° C and pressures in the range of around 8 to 10 kbar. There it is mostly found in drusen as a deposit from the gas phase and a matrix of rhyolite and dacite .

In addition to its type locality Sakkabira on Ōsumi, Osumilitn was also found in Japan on Sakurajima and the Aira caldera on Kyūshū.

So far (as of 2010) the mineral has been found at 26 sites around the world: In the Antarctic region of Enderbyland ; at the Zinster Kuppe ( Kemnath , Bavaria), the Blauen Kuppe ( Eschwege , Hessen) and at the Ettringer Bellerberg ( Ettringen , Rhineland-Palatinate) in Germany; on Mont Denise near Espaly-Saint-Marcel in the French Haute-Loire department ; on the Pauliberg in Austria; at Visakhapatnam in India; on Vesuvius and Monte Arci in Italy; in the Canadian province of Labrador ; on the North Island in New Zealand; in the Norwegian province of Rogaland ; in the Aldan highlands (Eastern Siberia) in Russia; in Namaqualand in South Africa; in the Tajik part of the Alai Mountains ; on the Labwor Hill in Uganda and near Tarpa in the Hungarian Szabolcs-Szatmár-Bereg County .

See also

literature

Web links

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

Individual evidence

  1. ↑ a b IMA / CNMNC List of Mineral Names (2012) - Osumilite (English, PDF 1.8 MB; p. 211)
  2. ↑ a b Webmineral - Osumilite- (Fe)
  3. ↑ a b American Mineralogist Crystal Structure Database - Osumilite (English, 2008)
  4. ↑ a b c d e f Osumilite , in: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 78.7 kB )
  5. ↑ American Mineralogist Crystal Structure Database - Osumilite (English, 2008)
  6. ↑ Denny Loose: Pan-African ultra-high temperature metamorphosis of archaic rocks of the Labwor Hills (Uganda) ( Memento from February 26, 2016 in the Internet Archive ) (PDF 26.6 kB; p. 2)
  7. ↑ Locations for Osumilith at the Mineralienatlas and at Mindat