Berezanskit

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Berezanskit
General and classification
other names

IMA 1996-041

chemical formula K Ti 4+ 2 Li 3 Si 12 O 30
Mineral class
(and possibly department) 		Silicates and germanates - ring silicates
System no. to Strunz
and to Dana 		9.CM.05 ( 8th edition : VIII / E.22)
63.02.01a.15
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  = 9.898  Å ; c  = 14.276 Å
Formula units Z  = 2
Physical Properties
Mohs hardness 2.5 to 3
Density (g / cm 3 ) measured: 2.66; calculated: 2.674
Cleavage perfect after {0001}
colour colorless
Line color White
transparency transparent
shine Glass gloss
Crystal optics
Refractive indices n ω  = 1.635
n ε  = 1.630
Birefringence δ = 0.005
Optical character uniaxial negative, rarely weakly biaxial
Other properties
Special features bright, bluish white fluorescence under short-wave UV light

The mineral Berezanskit is a very rarely occurring ring silicate from the milarite group and has the idealized chemical composition KTi 4+ 2 Li 3 Si 12 O 30 . It crystallizes in a hexagonal crystal system and develops aggregates of colorless, platy crystals less than a millimeter in size.

Berezansite forms in alkali-rich pegmatites at low pressure (<2 kbar ) and average temperatures around 450–500 ° C. It is so far only on its type locality , the moraines of the Darai-Pioz- glacier in Alay Mountains in Tajikistan have been found.

Etymology and history

Was discovered Berezanskit in a fragment of a potassium and sodium-rich Pegmatites in the moraines of the Darai-Pioz- glacier in Alay Mountains in Tajikistan and in 1997 by LA Pautov, AA Agakhanov described as a new mineral of Milaritgruppe. They named the mineral after the Russian geologist Anatolyi Vladimirovich Berezansky, who had mapped the region.

classification

In the outdated, but still partially common 8th edition of the mineral classification by Strunz Berezanskit belongs Almarudit , Armenit , Brannockit , Chayesit , Darapiosit , Dusmatovit , Emeleusit , Faizievit , Merrihueit , Oftedalit , Osumilith , Osumilith- (Mg) , Poudretteit , Roedderit , Sogdianite , sugilite , trattnerite and yagiite to the general division of " ring silicates (cyclosilicates)" in the " milarite-osumilite group " with system no. VIII / E.22 .

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 assigns the Berezansite to the "ring silicates" section. This is, however, further subdivided according to the structure of the rings, so that the mineral can be found in the sub-section "[Si 6 O 18 ] 12− -six double rings" according to its structure . It includes Agakhanovit-Ce , Almarudit, Armenit, Brannockit, Chayesit, Eifelit , Darapiosit, Dusmatovit, Friedrichbeckeit , Klöchit , Merrihueit, Milarit, Oftedalit, Osumilith, Osumilith- (Mg), Poudretteit, Roedderit, Shibkovite , Sugilite Trattnerite and Yagiite to the " Milarite group " with the system no. 9.CM.05 .

Also the systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Berezanskit to the class of "silicates and germanates", but there in the more finely subdivided 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”.

Chemism

Berezanskite is the titanium analogue of Brannockite or Sogdianite and the measured composition from the type locality is [12] (K 0.98 Ba 0.01 ) [9] Na 0.06 [6] (Ti 1.94 Nb 0.04 Fe 0.02 ) [4] (Li 2.95 Al 0.02 ) [4] Si 11.99 O 30 , the coordination number of the respective position in the crystal structure being given in square brackets .

Berezansite forms mixed crystals with Brannockite, Sogdianite and Sugilite, which manifests itself in the replacement of Ti 4+ by Sn 4+ and Zr 4+ as well as the coupled incorporation of Fe 3+ and Na + .

Crystal structure

Berezanskite crystallizes in the hexagonal crystal system in the space group P 6 / mcc (space group no. 192) with the lattice parameters a  = 9.898  Å and c  = 14.276 Å as well as two formula units per unit cell .  Template: room group / 192

The weak, optically biaxial character of Berezanskit suggests a possibly lowered symmetry.

Berezanskite is isotypic to milarite , ie it crystallizes with the same structure as milarite. The 12-fold coordinated C-position is fully occupied with potassium (K + ) and the 9-fold coordinated B-position is vacant. Titanium (Ti 4+ ) and traces of niobium (Nb 4+ ) and iron (Fe 3+ ) fill the 6-fold coordinated A position. The tetrahedrally coordinated T2 position contains only lithium (Li + ). The T1 position, which builds up the 6 double rings, only contains silicon (Si 4+ ).

Education and Locations

Berezansite forms in alkali-rich , H 2 O-undersaturated pegmatites at low pressure (<2 kbar ) and temperatures around 450–500 ° C.

So far Berezanskit was only at its type locality , the Darai-Pioz- glacier in Alay Mountains in Tajikistan found and documented, where in pegmatitic rocks in the moraine occurs. Berezanskit occurs here together with quartz , microcline , the sodium pyroxene aegirine , the lithium mica polylithionite , Cs- cuplet kit , a chain silicate from the astrophyllite group, the 4- ring silicate hyalotekite , the 5-chain silicate Tadzhikit- (Y) , the 6- ring silicate Double chain silicate zektzerite , the island silicate stillwellite (Ce) the milarite group mineral dusmatovite and pyrophanite as well as the branched 6-ring silicate tienshanite .

This very mineral-rich site represents the type locality of 35 minerals (as of 2016), 5 of them from the milarite group alone: ​​Berezanskite, Darapiosit , Dusmatovite , Shibkovite and Sogdianite . Furthermore, the milarite group minerals milarite, osumilite and sugilite were detected here.

See also

literature

Web links

Individual evidence

  1. ↑ a b c d e f g h i j k l m n o p q r LA Pautov, AA Agakhonov (1997): Berezanskite, K Li3 Ti2 Si12 O30, a new mineral , In: Zapiski Vseross. Mineral. Obshch. , 126 (4), pp. 75–80 ( PDF (English summary), 95 kB )
  2. ↑ a b c d e f g h i j k l m n o p J. Jambor et al. (1998): New Mineral Names - Berezanskite Abstract in: American Mineralogist , 83, p. 907 ( PDF, 71 kB )
  3. ↑ Webmineral - Berezanskit (English)
  4. ↑ a b c d e FC Hawthorne, E. Sokolova, LA Pautov, AA Agakhanov and V.Yu. Karpenko (2016): Prepublication: Refinement of the crystal structure of berezanskite, Ti 2 □ 2 K Li 3 (Si 12 O 30 ) , In: Mineralogical Magazine ( PDF (1.3 MB) )
  5. ↑ a b Darai-Pioz Glacier (Dara-i-Pioz; Dara-Pioz), Alai Range (Alayskiy), Tien Shan Mtn, Region of Republican Subordination, Tajikistan