Crossbowite

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Crossbowite
General and classification
other names

IMA 2005-035

chemical formula K 5 Na 6 Mn 3+ Mn 14 2+ [Si 9 O 22 ] 4 (OH) 10 · 4H 2 O
Mineral class
(and possibly department)
Silicates and germanates - layered silicates
System no. to Strunz
and to Dana
9.EG.65 ( 8th edition : VIII / H.17)
01/74/03/02
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group C 2 / m (No. 12)Template: room group / 12
Lattice parameters a  = 17.333  Å ; b  = 23.539 Å; c  = 13.4895 Å
β  = 115.069 °
Formula units Z  = 2
Physical Properties
Mohs hardness 3.5
Density (g / cm 3 ) Please complete!
Cleavage Please complete!
colour dark reddish brown to copper red
Line color light brown
transparency translucent, also transparent in thin layers
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.532
n β  = 1.560
n γ  = 1.564
Birefringence δ = 0.032
Optical character biaxial negative
Axis angle 2V = measured: 10 to 20 °
Pleochroism strong: X = light yellowish brown, Y and Z = dark reddish brown

The mineral armbrusterite is a very rarely occurring sheet silicate with the chemical composition K 5 Na 6 Mn 3+ Mn 14 2+ [Si 9 O 22 ] 4 (OH) 10 · 4H 2 O. It crystallizes in the monoclinic crystal system and was previously only able to Form of tiny, translucent and reddish-brown crystals less than a millimeter in size can be discovered.

Etymology and history

Armbrusterite was first discovered in 2005 on Mount Kukiswumtschorr in the Chibinen (English: Khibiny massif ) on the Russian Kola Peninsula . The mineral was analyzed and described by a research team consisting of the mineralogists and geologists Victor N. Yakovenchuk, Sergey V. Krivovichev, Yakov A. Pakhomovsky, and Gregory Yu. Ivanyuk, Ekaterina A. Selivanova, Yury P. Menʼshikov and Sergey N. Britvin, who named it after the Bern mineralogist Thomas Armbruster , for his outstanding contributions to structural mineralogy and crystallography, especially the study of manganese-rich minerals, as well as his constant efforts to improve them Cooperation with the former Soviet Union.

Armbrusterite was recognized as an independent mineral by the International Mineralogical Association (IMA) in the same year under the internal accession number (IMA) 2005-035 .

classification

Since the armbrusterite was only discovered and recognized in 2005, it is not listed in the Strunz mineral system (8th edition), which has been outdated since 2001 . Only in the "Lapis Mineralienverzeichnis", published in 2008, which, out of consideration for private collectors and institutional collections, is still based on the classic systematics of Karl Hugo Strunz , was the mineral given system no. VIII / H.17-55 .

The 9th edition of Strunz's mineral systematics , which has been valid since 2001 and is used by the IMA, assigns the armbrusterite to the class of "silicates and germanates" and there in the department of "phyllosilicates". This division is further subdivided according to the type of crystal structure, so that the mineral, according to its structure, can be found in the sub-division “phyllosilicates with double networks and six-fold rings”, where it is the only member of the unnamed group 9.EG.65 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , also assigns the armbrusterite to the class of "silicates and Germanates" and there in the section of "layered silicates with modulated layers". Here it can be found together with Parsettensit in the unnamed group 74.01.03 within the subsection “ Layered silicates: modulated layers with connected islands ”.

Crystal structure

Armbrusterite crystallizes monoclinically in the space group C 2 / m (space group no. 12) with the lattice parameters a  = 17.333  Å ; b  = 23.539 Å; c  = 13.4895 Å and β = 115.069 ° as well as 2 formula units per unit cell . Template: room group / 12

Education and Locations

Armbrusterite forms in cancrinite - aegirine - microcline veins together with urtite and in close connection with rait .

So far, armbrusterite could only be found at its type locality Kukiswumtschorr in Russia and in rock samples from the "AKH49" borehole near Dingleton (formerly Sishen ) in the South African province of North Cape.

See also

Web links

Individual evidence

  1. a b c d e f g h i Victor N. Yakovenchuk, Sergey V. Krivovichev, Yakov A. Pakhomovsky, Gregory Yu. Ivanyuk, Ekaterina A. Selivanova, Yury P. Menʼshikov, Sergey N. Britvin: Armbrusterite, K 5 Na 6 Mn 3+ Mn 2+ 14 [Si 9 O 22 ] 4 (OH) 10 · 4 H 2 O, a new Mn hydrous heterophyllosilicate from the Khibiny alkaline massif, Kola Peninsula, Russia . In: American Mineralogist. 2007, 92, pp. 416–432 ( full text ; PDF; 398 kB).
  2. Webmineral - Armbrusterite (English)
  3. Mindat - Armbrusterite (English)