Fluoromayenite

from Wikipedia, the free encyclopedia
Fluoromayenite
General and classification
other names

IMA 2013-019

chemical formula Ca 12 Al 14 O 32 [□ 4 F 2 ]
Mineral class
(and possibly department) 		Silicates and Germanates
Similar minerals Fluorocyuygenite
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic-hexakistrahedral; 4  3  m
Space group I 4 3 d (No. 220)Template: room group / 220
Lattice parameters a  = 11.9894 (natural); synthetic: 11.970  Å
Formula units Z  = 2
Physical Properties
Mohs hardness 5.5 - 6
Density (g / cm 3 ) calculated: 2.745
Cleavage no
colour colorless, rarely pale green or yellow
Line color White
transparency transparent
shine Glass gloss
radioactivity -
magnetism -
Crystal optics
Refractive index n  = 1.612
Birefringence none, isotropic

The mineral fluoromayenite is a rarely occurring oxide from the mayenite upper group with the idealized chemical composition Ca 12 Al 14 O 32 F 2 . It crystallizes in the cubic crystal system with the structure of chloromayenite .

Fluoromayenite only develops very small, colorless crystals or round grains less than 0.1 mm in size. As far as formed, the crystals show surfaces of the triakis tetrahedron {211}.

Fluoromayenite is formed at low pressure and high temperatures when calcium-rich sediments are converted by a fluorine-rich fluid . At lower temperatures and in the presence of water, fluoromayenite is converted to fluorinated cyuygenite .

Etymology and history

A cubic calcium aluminate has been known since the beginning of the 20th century, for which the composition 5CaO * 3Al 2 O 3 was given at the time. Since calcium aluminates are important compounds in cement clinker, they have been intensively studied since then.

The structure of this compound was elucidated in 1936 by W. Büssem and A. Eitel at the Kaiser Wilhelm Institute for Silicate Research in Berlin-Dahlem . In the course of the structure elucidation, they corrected the composition to 12CaO * 7Al 2 O 3 , C 12 A 7 in the cement chemical notation .

The first finds of a natural, cubic calcium aluminate were made in 1963 by L. Heller in a Sprurrite rock in the Nalhal Ayalon outcrop of the Hatrurim Formation in Israel. It is a common mineral found in many outcrops of the Hatrurim Pyromethamorphic Formation.

A year later it was described as a new mineral by Gerhard Hentschel together with brownmillerite in limestone inclusions from lavas from Ettringer Bellerberg with the composition Ca 12 Al 14 O 33 . He named the new mineral after the nearby town of Mayen Mayenite .

The fluorine analog of mayenite, the compound 11CaO * 7Al 2 O 3  * CaF 2 , was synthesized in 1973 by PP Williams of the DSIR in Petone , New Zealand , and the structure was examined.

In the course of the redefinition of the Mayenite upper group since 2010, Mayenites from various sites were re-examined. All naturally occurring mayenites contain fluorine or chlorine and the composition given by Hentschel could not be confirmed in any case. Mayenite was then discarded as a mineral name, new names introduced and new minerals of the mayenite group discovered, including fluoromayenite:

  • Chloromayenite for mayenite with the composition Ca 12 Al 14 O 32 [□ 4 Cl 2 ], z. B. from Ettringer Bellerberg
  • Chlorkyuygenit for hydrated chloromayenite (Ca 12 Al 14 O 32 [(H 2 O) 4 Cl 2 ])
  • Fluoromayenite for mayenite with the composition Ca 12 Al 14 O 32 [□ 4 F 2 ], z. B. from Jebel Harmun of the Hatrurim formation in Palestine
  • Fluorocyuygenite for hydrated fluoromayenite (Ca 12 Al 14 O 32 [(H 2 O) 4 F 2 ])

classification

In the current classification of the International Mineralogical Association (IMA), fluoromayenite belongs to the mayenite group with less than 4 Cl and 2 Si per formula unit together with chlormayenite , chlororkyuygenite and fluorokyuygenite in the mayenite upper group.

The outdated, but still in use 8th edition of the mineral classification according to Strunz does not list the fluoromayenite. As a fluorine analog of chloromayenite, it would be part of the "Brownmillerite Mayenite Group" with system no. IV / A.07 in the department of “Oxides and Hydroxides”.

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), does not yet know the fluoromayenite either. Here he would with Mayenit in the unnamed group with the system no. 4.CC.20 in the department of "oxides (hydroxides, V [5,6] -vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)".

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , does not yet list the fluoro mayenite. Together with Mayenit he would be grouped in the unnamed group 11/07/03 of the department of "Multiple Oxides".

Chemism

Fluoromayenite with the idealized composition [X] Ca 12 [T] Al 3+ 14 O 32 [W] [□ 4 F 2 ] is the fluorine analog of chloromayenite ( [X] Ca 12 [T] Al 3+ 14 O 32 [W] [□ 4 Cl 2 ]), where [X], [T] and [W] are the positions in the mayenite structure and □ (blank) stands for an unoccupied grid position.

The composition from the type locality is

  • [X] (Ca 11.951 Na 0.037 ) [T] (Al 13.675 Fe 3+ 0.270 Mg 0.040 Si 0.009 P 0.005 S 6+ 0.013 ) O 31.503 (OH) 1.492 [W] [□ 4.581 F 1.375 Cl 0.044 ]

The deviations from the ideal composition are essentially due to two rows of mixed crystals. On the one hand, Fe 3+ is incorporated in the [T] positions, corresponding to the exchange reaction

  • [T] Al = [T] Fe 3+ (hypothetical Fe analog of fluoromayenite),

on the other hand, the mixture with the hypothetical (OH) analogue [X] Ca 12 [T] Al 3+ 14 O 30 (OH) 6 [W] [□ 6 ] leads to an exchange of oxygen (O 2- ) and fluorine ( F - ) through 3 (OH) according to the reaction

  • [O2] O 2- + 3 [O2a] □ + [W] F - = [O2] □ + 3 [O2a] (OH) - + [W] □.

Crystal structure

Fluoromayenite crystallizes with cubic symmetry in the space group I 4 3 d (space group no. 220) with 2 formula units per unit cell . The natural mixed crystal from the type locality has the lattice parameter a  = 11.9894  Å . Template: room group / 220

The structure is that of chlormayenite . Aluminum (Al 3+ ) occupies the two tetrahedral Z-positions surrounded by 4 oxygen ions. They form a tetrahedral structure that encloses interconnected cages. Each of these cages is filled with two calcium (Ca 2+ ) ions, which are irregularly surrounded by 6 oxygen. In their center between the calcium ions, 1/3 of the cages contain a fluorine ion (F - ).

The substitution of an oxygen in the O2 position and a fluorine ion in the W position by three OH groups in the otherwise unoccupied O2a position leads to an increase in the coordination number of the neighboring aluminum in a T1 position from 4 to 6. In the fluoromayenite of the type locality In this way, around 11% of the aluminum ions on T1 are octahedrally coordinated by 6 oxygen.

Education and Locations

Fluoromayenite forms pyrometamorphically at low pressure and high temperatures when calcium-rich sediments are converted by a fluorine-rich fluid . By water-rich fluids Fluormayenit can be converted into Fluorkyuygenit and katoite - Grossular -Mischkristalle.

Fluoromayenite has so far (2018) only been detected in two outcrops of the Hatrurim Formation in Palestine and Jordan . In its type locality , the Jebel Harmun Hatrurim the formation far from the village Nabi Musa, West Bank in Palestine, occurs Fluormayenit as inclusion in ye'elimite on or fills interstices between Larnite , brownmillerite and Fluorellestadit . More Begleitminerale are fluorapatite , Srebrodolskit , Shulamitit , Harm Unit , spinel , Magnesioferrit , gehlenite , periclase , Ternesit , Nabimusait , oldhamite , barite , Vorlanit , Vapnikit , chalcocite and covellite .

Web links

Individual evidence

  1. ↑ Fluoromayenites. In: mindat.org. Hudson Institute of Mineralogy, accessed May 25, 2019 .
  2. ↑ 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 ab Evgeny V. Galuskin, Frank Gfeller, Thomas Armbruster, Irina O. Galuskina, Yevgeny Vapnik, Mateusz Dulski , Mikhail Murashko, Piotr Dzierzanowsky, Viktor V. Sharygin, Sergey V. Krivovichev and Richard Wirth: Mayenite supergroup, part III: Fluormayenite, Ca12Al14O32 [ 〈4 F2], and fluorkyuygenite, Ca12Al14O32 [(H2O) 4F2], two new minerals from pyrometamorphic rocks of the Hatrurim Complex, South Levant . In: European Journal of Mineralogie . tape 27 , 2015, p. 123-136 ( researchgate.net [PDF; 689 kB ; accessed on July 28, 2018]).
  3. ^ A b PP Williams: Refinement of the structure of 11CaO.7Al2O3.CaF2 . In: Acta Crystallographica Section B . B29, 1973, p. 1550–1551 , doi : 10.1107 / S0567740873004942 .
  4. ↑ Ernest Stanley Shepherd and GS Rankin: The binary systems of alumina with silica, lime, and magnesia; with optical study by Fred. Eugene Wright . In: American Journal of Science . tape 28 , 1909, pp. 293-333 , doi : 10.2475 / ajs.s4-28.166.293 .
  5. ↑ a b W. Büssem, A. Eitel: The structure of Pentacalciumtrialuminats . In: Journal of Crystallography . tape 95 , 1936, pp. 175–188 ( rruff.info [PDF; 628 kB ; accessed on July 22, 2018]).
  6. ^ S. Gross: The mineralogy of the Hatrurim formation, Israel. In: Geol. Surv. Isr. Bull. Band 70 , 1977, pp. 1–80 ( rruff.info [PDF; 5.7 MB ; accessed on July 29, 2018]).
  7. ↑ Michael Fleischer: New Mineral Names - Mayenite . In: The American Mineralogist . tape 50 , 1965, pp. 2096–2111 ( rruff.info [PDF; 1,3 MB ; accessed on July 29, 2018]).
  8. ↑ a b c d Evgeny V. Galuskin, Frank Gfeller, Irina O. Galuskina, Thomas Armbruster, Radu Bailau and Viktor V. Sharygin: Mayenite supergroup, part I: Recommended nomenclature . In: European Journal of Mineralogie . tape 27 , 2014, p. 99-111 ( cnmnc.main.jp [PDF; 802 kB ; accessed on April 29, 2020]).
  9. ↑ EV GALUSKIN, J. KUSZ, T. Armbruster, R. BAILAU, IO GALUSKINA, B. TERNES AND M. Murashko: A reinvestigation of mayenite from the type locality, district Ettringer the Bellerberg volcano near Mayen, Eifel, Germany . In: Mineralogical Magazine . tape 76 , 2012, p. 707-716 ( rruff.info [PDF; 388 kB ; accessed on July 29, 2018]).
  10. ↑ EV Galuskin, IO Galuskina, J. Kusz, F. Gfeller, T. Armbruster, R. Bailau, M. Dulski, VM Gazeev, NN Pertsev, AE Zadov, P. Dzierzanowski: supergroup Mayenite, part II: Chlorkyuygenite from northern Caucasus Kabardino-Balkaria, Russia, a new microporous mayenite supergroup mineral with `` zeolitic '' H2O. In: European Journal of Mineralogie . tape 27 , 2015, p. 123-136 , doi : 10.1127 / ejm / 2015 / 0027-2419 ( researchgate.net ).