Shepherdite

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

IMA1997-048

chemical formula Ca 2+ 2 Na + Mg 2+ 2 V 5+ 3 O 12
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. according to Strunz 8.AC.25 ( 8th edition : 7 / A.08-45)
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic hexakisoctahedral; 4 / m  3  2 / m
Space group Ia 3 d (No. 230)Template: room group / 230
Lattice parameters a  = 12.437 (synthetic),
12.427 (natural mixed crystal)  Å
Formula units Z  = 8
Frequent crystal faces Deltoidalicositetrahedron {211}, rhombic dodecahedron {110}, cube {100}
Physical Properties
Mohs hardness 5
Density (g / cm 3 ) natural mixed crystal: 3.40 (measured), 3.43 (calculated),
3.431 (synthetic)
Cleavage no
Break ; Tenacity shell-like
colour Orange red
Line color yellow
transparency Please complete!
shine Please complete!
Crystal optics
Refractive index n  = 1.94 (natural mixed crystal)
Birefringence isotropic

The mineral shepherdite is an extremely rare vanadate from the upper group of the garnet and has the idealized chemical composition Ca 2+ 2 Na + Mg 2+ 2 V 5+ 3 O 12 . It crystallizes in the cubic crystal system with the structure of garnet.

Shepherdite occurs in the form of orange-red, glass-shining crystals less than a millimeter in size. The crystal shape is dominated by the deltoidalikositetrahedron {211} with smaller rhombic dodecahedron faces { 110} and cube faces {100}.

Schäferite is formed during the contact metamorphosis of silicate-rich rocks by alkali-rich basaltic magmas. The type locality and the only known natural site so far (2018) are xenolites of the Bellerberg volcano in the Eifel , Rhineland-Palatinate in ( Germany ).

Etymology and history

Various vanadates with a garnet structure have been synthesized since the 1960s. Tetrahedrally coordinated V 5+ is an efficient luminescence center. For this reason and because of their high chemical stability, vanadium garnets are still of technical interest as yellow or white phosphors for light-emitting diodes .

Calcium-sodium-magnesium-vanadate of natural origin was only found in the Eifel in 1999 and described by W. Krause, G. Blass and H. Effenberger. They named the new mineral from the Berzeliit group after the collector Helmut Schäfer, who discovered it in the xenolites of the Bellerberg basalt. In the following years these collectors discovered shepherdite in other basalts in the Eifel.

In 2017, an artificial equivalent of shepherdite was discovered in an old slag dump in Greece.

classification

The current classification of the International Mineralogical Association (IMA) counts the shepherdite to the garnet upper group, where together with berzeliite , manganese berzeliite and palenzonaite it forms the berzeliite group with 15 positive charges on the tetrahedrally coordinated lattice position.

In the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the shepherdite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the department of "anhydrous phosphates [PO 4 ] 3− , without foreign anions", where he together with Berzeliit, Chladniit , Fillowit , Galileiit , Johnsomervilleit , Manganberzeliit , Palenzonait, Storneseit- (Y) and Xenophyllite formed the unnamed group VII / A.08 .

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 shepherdite to the category of “phosphates etc. without additional anions; without H 2 O “. This is, however, further subdivided according to the relative size of the cations involved , so that the mineral can be found according to its composition in sub-section C "With medium-sized and large cations", where berzeliite , manganese berzelite and palenzonaite make up the berzeliite group 8.AC.25 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns shepherdite to the class of "phosphates, arsenates and vanadates" and there in the department of "anhydrous phosphates etc.". Here it is together with berzeliite, manganese berzeliite and palenzonaite in the Berzeleiite group systematics of minerals according to Dana / Phosphate, Arsenate, Vanadate # 38.02.01 Berzeliite group within the subdivision "38.02 Anhydrous phosphates etc., (A + B 2+ ) 5 (XO 4 ) 3 ”.

Chemism

Schäferite with the idealized composition [X] (Na + Ca 2+ 2 ) [Y] Mg 2+ 2 [Z] V 5+ 3 O 12 is the magnesium analog of palenzonaite ( [X] (Na + Ca 2+ 2 ) [Y] Mn 2+ 2 [Z] V 5+ 3 O 12 ) or the vanadium analogue of berzeliite ( [X] (Na + Ca 2+ 2 ) [Y] Mg 2+ 2 [Z] As 5 + 3 O 12 ).

The composition from the type locality is - [X] (Ca 2+ 2.09 Na + 0.73 □ 0.10 Mg 2+ 0.04 Mn 2+ 0.02 Fe 2+ 0.01 ) [Y] Mg 2 + 2 [Z] (V 5+ 2.96 P 5+ 0.02 Si 4+ 0.01 ) O 12

Both the natural shepherdite and its synthetic equivalent can contain vacancies in the X and Y positions, corresponding to an exchange reaction - 2 [X] Na = [X] (Ca, Mg, Mn) + [X] □

Almost 10% of the vanadium can be replaced by phosphorus, according to the reaction: - [Z] V 5+ = [Z] P 5+

In shepherds made from slag from ancient metal smelting in Greece, the exchange reaction - [X] Ca 2+ + [Y] (Mg, Ni) 2+ = [X] Na + + [Y] Fe 3+

observed.

Schäferite crystallizes with the same structure as silicate garnets, but like all garnets of the Berzeleiite group it contains only small amounts of silicon. There is no extensive miscibility between silicate and vanadate grenades or arsenate grenades.

Crystal structure

Schäferite crystallizes with cubic symmetry in the space group Ia 3 d (space group no. 230) with 8 formula units per unit cell . The natural mixed crystal from the type locality has the lattice parameter a  = 12.427  Å . The lattice parameter of synthetic, pure schäferite is somewhat larger: a  = 12.437 Å. Template: room group / 230

The structure is that of garnet . Sodium (Na + ) and calcium (Ca 2+ ) occupy the dodecahedral X-position surrounded by 8 oxygen ions, magnesium (Mg 2+ ) the octahedral Y-position surrounded by 6 oxygen ions and the tetrahedral Z-position surrounded by 4 oxygen ions is exclusive occupied with vanadium (V 5+ ).

Education and Locations

Natural shepherdite is formed in contact metamorphosis when SiO 2 -rich xenolites are overprinted by alkali-rich, basaltic magmas.

The type locality is the Caspar basalt quarry on the Bellerberg volcano in the Eifel , Rhineland-Palatinate in ( Germany ). Here, shepherdite is found in xenolites together with magnesioferrite , quartz , albite and pseudobroockite . Comparable occurrences are only known from the Eifel. Shepherdite was still found here on the Nickenicher Sattel (Eicher Sattel) near Andernach and in the Rothenberg quarry near Mendig .

Shepherdite-rich vanadium garnets of artificial origin were found in the Liebenbergite slags at Agios Konstantinos in the Lavrion District in the Attica region , Greece . Schäferite occurs here together with Liebenbergite, Trevorite , Bannermanite and other synthetic equivalents of nickel-vanadium minerals as well as Albite, Nosean and Haüyn .

See also

Web links

Individual evidence

  1. ↑ a b c d e f g h i j k l m n o p q r s t u John L. Jambor, Vladimir A. Kovalenker and Andrew C. Roberts: New Mineral Names: Schäferite . In: American Mineralogist . tape 84 , 1999, pp. 1685–1688 ( minsocam.org [PDF; 33 kB ; accessed on March 17, 2018]).
  2. ↑ a b c d G. Oversluizen and R. Metselaar: ESR and optical absorption spectra of reduced vanadium ions in Ca2NaMg2V3O12 garnet . In: J. Phys. C: Solid State Phys. tape 15 , 1982, pp. 4869-4880 ( semanticscholar.org [PDF; 694 kB ; accessed on March 17, 2018]).
  3. ↑ a b c List of places where shepherdite was found in the Mineralienatlas and Mindat
  4. ↑ Gerhard Bayer: vanadate A3B2V3O12 with Garnet Structure . In: Journal of the American Ceramic Society . tape 11 , 1965, doi : 10.1111 / j.1151-2916.1965.tb14681.x .
  5. ↑ a b Akihiko Nakatsuka, Yasuaki Ikuta, Akira Yoshiasa and Kazuake Iishi: Vanadate garnet, Ca2NaMg2V3O12 . In: Acta Crystallographica Section C . C59, 2003, p. i133-i135 , doi : 10.1107 / S0108270103023035 .
  6. ↑ Yanlin Huang, Young Moon Yu, Taiju Tsuboi, Hyo Jin Seo: Novel yellow-emitting phosphors of Ca5 M4 (VO4) 6 (M = Mg, Zn) with isolated VO4 tetrahedra . In: Optics Express . tape 20 , 2012 ( osapublishing.org [PDF; 1,2 MB ; accessed on March 22, 2018]).
  7. ↑ a b c Natalia N. Koshlyakova, Natalia V. Zubkova, Igor V. Pekov, Gerald Giester, Dmitry Yu. Pushcharovsky, Nikita V. Chukanov, Panagiotis Voudouris, Andreas Magganas, Athanassios Katerinopoulos: Crystal chemistry of vanadate garnets from old metallurgical slags of Lavrion, Greece . In: New Yearbook of Mineralogy - Papers: Journal of Mineralogy and Geochemistry . tape 194 , 2017, p. 19-25 , doi : 10.1127 / njma / 2016/0010 .
  8. ^ Edward S. Grew, Andrew J. Locock, Stuart J. Mills, Irina O. Galuskina, Evgeny V. Galuskin and Ulf Hålenius: IMA Report - Nomenclature of the garnet supergroup . In: American Mineralogist . tape 98 , 2013, p. 785–811 ( main.jp [PDF; 2,3 MB ; accessed on July 8, 2017]).
  9. ^ Andrew J. Locock: An Excel spreadsheet to recast analyzes of garnet into end-member components, and a synopsis of the crystal chemistry of natural silicate garnets . In: Computers & Geoscience . tape 34 , 2008, p. 1769–1780 ( mcgill.ca [PDF; 294 kB ; accessed on April 7, 2018]).
  10. ^ Photos by Schäferit at Mindat