Agakhanovite- (Y)
| Agakhanovite- (Y) | |
|---|---|
| General and classification | |
| other names |
IMA 2013-090 |
| chemical formula | (YCa) □ 2 KBe 3 Si 12 O 30 |
|
Mineral class (and possibly department) |
Silicates and germanates - ring silicates |
| System no. according to Strunz | 9.CM.05 |
| Similar minerals | Milarite |
| Crystallographic Data | |
| Crystal system | hexagonal |
| Crystal class ; symbol | dihexagonal-dipyramidal; 6 / m 2 / m 2 / m |
| Space group | P 6 / mcc (No. 192) |
| Lattice parameters | a = 10.3476 Å ; c = 13.7610 Å |
| Formula units | Z = 2 |
| Frequent crystal faces | {100}, {001} |
| Twinning | - |
| Physical Properties | |
| Mohs hardness | 6th |
| Density (g / cm 3 ) | calculated: 2.672 |
| Cleavage | not observed |
| Break ; Tenacity | shell-like |
| colour | colorless |
| Line color | White |
| transparency | transparent |
| shine | Glass gloss |
| Crystal optics | |
| Refractive indices |
n ω = 1.567 n ε = 1.564 |
| Birefringence | δ = 0.003 |
| Optical character | uniaxial negative |
| Pleochroism | - |
The mineral agakhanovite- (Y) is a very rarely occurring ring silicate from the milarite group with the idealized chemical composition (YCa) □ 2 KBe 3 Si 12 O 30 . It crystallizes in the hexagonal crystal system and develops colorless, prismatic crystals less than a millimeter in size.
Agakhanovit- (Y) is found as late deposition from hydrothermal solutions in Miarolen of yttrium - and beryllium -rich, granitic pegmatites . In addition to its type locality , the cleavelandite - amazonite pegmatite in Tørdal , southern Norway , yttrium-rich milarites have so far only been detected in a few other localities: the jaguaraçú pegmatite (Minas Gerais, Brazil), the pegmatites of the Strange Lake complex (Québec and Labrador , Canada) and the Velká-Skála-Pegmatite ( Jihočeský kraj , Czech Republic ).
Etymology and history
Yttrium- and beryllium-rich milarites were first described in 1965 by Oftedal and Sæbø from Grorud in Norway. In the 1990s, further discoveries of Y-milarites from Brazil (Jaguaraçú) and Canada (Strange Lake) followed, but these were chemically too inhomogeneous (zoned) for the definition of a new mineral.
It was not until 2011 that a homogeneous yttrium milarite crystal was isolated from the pegmatite near Tørdal, with which the complete characterization and then in 2013 the recognition of the new Y-Be mineral Agakhanovit- (Y) by the International Mineralogical Association (IMA) under the internal input -No. IMA 2013-090 succeeded.
The mineral was named after Atali A. Agakhanov (* 1971), a Russian mineralogist from the Fersman Museum in Moscow . Agakhanov worked on a variety of pegmatitic minerals, e.g. As in the investigation of pegmatites in the Darai-Pioz- glacier in Alay Mountains ( Tajikistan involved) and the first description of two new minerals of Milaritgruppe: Dusmatovit (1996) and Berezanskit (1997).
classification
Since the Agakhanovit- (Y) was only discovered in 2003, it is not listed in the outdated 8th edition of the mineral classification according to Strunz . Agakhanovit- (Y) was only given the system and mineral number in the "Lapis mineral directory", which was last updated in 2018 and, out of consideration for private collectors and institutional collections, is still based on the classic systematics of Karl Hugo Strunz . VIII / E.22-19 . In the "Lapis system" this corresponds to the section " Ring Silicates : Double Six Rings [Si 12 O 30 ] 12- ", where together with Almarudit , Armenit , Berezanskit , Brannockit , Chayesit , Darapiosit , Dusmatovit , Eifelit , Emeleusit , Faizievit , Friedrichbeckeit , Klöchit , Lipuit , Merrihueit , Milarit , Oftedalit , Osumilite , Osumilite- (Mg) , Poudretteit , Roedderite , Shibkovite , Sogdianite , Sugilite , Trattnerite , Yagiit and Yakovenchukit- (Y) form the "Milarite-Osumilite group".
The 9th edition of Strunz's mineral systematics , which has been valid since 2001 and is used by the IMA, also classifies Agakhanovite- (Y) in the "ring silicates" section. This is also 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 belongs to it with Almarudit, Armenit, Berezanskit, Brannockit, Chayesit, Darapiosit, Dusmatovit, Eifelit, Friedrichbeckeit, Klöchit, Merrihueit, Milarit, Oftedalit, Osumilith, Osumilith- (Mg), Poudretteit, Roedderit, Shibkovite, Sogdianit Yagiit to the " Milaritgruppe " with the system no. 9.CM.05 .
In the systematics of minerals according to Dana , which is mainly used in the English-speaking world , Agakhanovit- (Y) as well as in the outdated 8th edition of Strunz's systematics is not recorded.
Chemism
Agakhanovit- (Y) is the yttrium -Analog of Oftedalit and forms a solid solution series with Milarit according to the coupled-exchange reaction :
- [A] Ca 2+ + [T2] Al 3+ = [A] Y 3+ + [T2] Be 2+
The measured composition from the type locality is [C] K 1.00 [B] (H 2 O) 0.92 Na 0.02 [A] (Y 0.89 Yb 0.01 Ca 1.06 ) ∑1.96 [T2] (Be 2.93 Al 0.07 ) ∑3.00 [T1] Si 12.02 O 30 , where the position in the crystal structure is indicated in square brackets.
In addition to yttrium, small amounts of other rare earth elements can be incorporated, especially cerium (Ce), ytterbium (Yb), dysprosium (Dy), europium (Eu) and neodymium (Nd). Cer-rich milarites, the cerium contents of which exceed those of yttrium, were referred to as agakhanovite (Ce), although a description as a separate species is still pending.
Crystal structure
Agakhanovit- (Y) crystallizes in the hexagonal crystal system in the space group P 6 / mcc (space group no. 192) with the lattice parameters a = 10.3476 Å and c = 13.7610 Å as well as two formula units per unit cell .
Agakhanovite- (Y) is isotypic to milarite , i.e. H. it crystallizes with the same structure as milarite.
The 12-fold coordinated C position is fully occupied with potassium, the 9-fold coordinated B position is half occupied with H 2 O and small amounts of Na. The octahedrally coordinated A position is fully occupied by 1 Ca 2+ and 1 Y 3+ . In addition to beryllium, the T2 position contains only small amounts of Al 3+ and the T1 position, which builds up the double rings, contains only silicon (Si 4+ ).
Education and Locations
Agakhanovite- (Y) forms at low temperatures and pressures from hydrothermal residual solutions of yttrium- and beryllium-rich pegmatites and is mostly found there in druses .
The type locality is the cleavelandite-amazonite-pegmatite in Tørdal , southern Norway , where it can be found grown on milarite or Kristiansenite . Other localities are the Jaguaraçú pegmatite in Minas Gerais , Brazil , the pegmatites of the Strange Lake Complex in Québec and Labrador , Canada and the Velká Skála pegmatite in Jihočeský kraj , Czech Republic .
In the jaguaraçú pegmatite, yttrium-rich milarite occurs together with adulara , albite , hematite , muscovite , quartz and minasgeraisite . In the partially pegmatitic, alkali-rich granite of the Strange Lake Complex, it is found in miaroles together with quartz, albite, hematite and xenotime .
In the Velká-Skála pegmatite, agakhanovite (Y) occurs grown on milarite, which is poor in yttrium, together with potassium feldspar and quartz.
See also
Web links
Individual evidence
- ↑ a b c d e f g h i j k l m n o p q r s t u v w x y z aa FC Hawthorne, YA Abdu, NA Ball, P. Černý, R. Kristiansen: Agakhanovite- (Y) , ideally (YCa) □ 2 KBe3Si12O30, a new milarite-group mineral from the Heftetjern pegmatite, Tørdal, Southern Norway: Description and crystal structure . In: American Mineralogist . tape 99 , 2014, pp. 2084–2088 (English, full text ).
- ↑ a b c d e P. Černý, FC Hawthorne, JJ Jambor, and JD Grice: Yttrian milarite. In: Canadian Mineralogist . tape 29 , 1991, pp. 533-542 ( rruff.info [PDF; 992 kB ]).
- ↑ a b c M. Novák, J. Cícha, R. Čopjaková, R. Škoda, M. Vašinová Galiová: Primary (magmatic?) And hydrothermal milarite-group minerals from the Velká skála pegmatite, Písek pegmatite district, Czech Republic . In: Second Eugene E. Foord Pegmatite Symposium, July 15-19, 2016 Colorado School of Mines campus, Golden, Colorado . July 2016, p. 70–72 (English, researchgate.net [PDF; 17.2 MB ]).
- ^ I. Oftedal and PC Sæbø: Contributions to the mineralogy of Norway. 30. Minerals from nordmarkite druses. In: Norsk Geologisk Tidsskrift . tape 45 , 1965, p. 171–175 (English, uio.no [PDF; 403 kB ]).
- ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
- ↑ Webmineral - New Dana Classification of Silicates
- ^ Heftetjern pegmatite, Tørdal, Drangedal, Telemark, Norway
- ↑ Jaguaraçu pegmatite (José Miranda mine; José Pinto mine; Carneirinho mine), Jaguaraçu, Minas Gerais, Brazil
- ^ Strange Lake complex (Lac Brisson complex), Québec & Newfoundland and Labrador, Canada