Kerimasite

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Kerimasite
General and classification
chemical formula Ca 3 Zr 2 Fe 3+ 2 SiO 12
Mineral class
(and possibly department) 		Silicates and Germanates
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  = 12.598 (synthetic)
12.549 (natural)  Å
Formula units Z  = 8
Frequent crystal faces Deltoidicositetrahedron {211}
Physical Properties
Mohs hardness 7th
Density (g / cm 3 ) calculated: 4.105
Cleavage not observed
colour light to dark brown, synthetic end link is yellowish
Line color light brown
transparency Please complete!
shine Glass gloss
Crystal optics
Refractive index n  = 1.945 (measured)
Birefringence isotropic, partially birefringent

The mineral kerimasite , before 2010 also kimzeyite , kimzeyite-fe or ferri-kimzeyite , is a rare silicate from the upper group of garnets with the idealized chemical composition Ca 3 Zr 2 Fe 3+ 2 SiO 12 . It crystallizes in the cubic crystal system with the structure of garnet. The dark brown crystals are rarely larger than 0.1 mm and show deltoidic tetrahedron surfaces .

Apart from its type locality , the carbonatites from the Kerimasi volcano in the Ngorongoro district , Arusha region of Tanzania , Kerimasite has so far (as of 2017) only been described at seven other sites. Many of the garnets described as kimzeyite before 2010 are also kerimasite, including occurrences in carbonatites, basic to ultra-basic magmatites and skarns .

Etymology and history

Garnets rich in zirconium have been described around the world since the 1960s, albeit only at a few localities under the name Kimzeyite. Most of these kimzeyites contained more iron than aluminum, but the Fe 3+ terminal kerimasite was only described as a new mineral by Zaitsev and co-workers in 2010 and recognized by the International Mineralogical Association (IMA). It was named after the place where it was found, the Kerimasi volcano in the Ngorongoro district, Arusha region in Tanzania.

In the course of systematic investigations into the mixing behavior of grenades of the schorlomite group, kerimasite was synthesized in 1967 by Ito and Frondel and in 1993 by Yamakawa and his colleagues.

Current work is investigating kerimasite, elbrusite and other hafnium and zirconium- containing grenades with regard to their suitability for the final disposal of highly radioactive waste from nuclear power plants.

classification

The current classification of the International Mineralogical Association (IMA) counts the kerimasite to the garnet upper group, where together with irinarassite , hutcheonite , schorlomite , kimzeyite and toturite it forms the schorlomite group with 10 positive charges on the tetrahedrally coordinated lattice position.

The 9th edition of Strunz's mineral systematics, which has been valid since 2001 and is used by the (IMA), does not list the kerimasite. Here it would be classified under the category of "island silicates (nesosilicates)". This is further subdivided according to the possible presence of further anions and the coordination of the cations involved , so that the mineral is classified according to its composition in the subsection “Island silicates without additional anions; Cations in octahedral [6] and usually greater coordination “would be found, where it would be found together with almandine, andradite, calderite, goldmanite, grossular, henritermierite, holtstamite, katoite, kimzeyite, knorringite, majorite, morimotoite, pyrope, schorlomite, spessartine and Uwarowit the "garnet group" with the system no. 9.AD.25 made. The garnet compounds blythite, hibschite, hydroandradite and skiagite, which are no longer regarded as minerals, were also included in this group. Wadalite , at that time still grouped with the grenades, proved to be structurally different and is now assigned to a separate group with chloromayenite and fluoromayenite . The garnets irinarassite , hutcheonite , toturite , menzerite (Y) and eringaite described after 2001 would, however, have been sorted into the garnet group.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , would also classify the kerimasite in the category of "island silicate minerals ". Here it would be together with schorlomite, kimzeyite and morimotoite in the "garnet group (schorlomite-kimzeyite series)" with the system no. 51.04.03c within the subsection “ Island silicates: SiO 4 groups only with cations in [6] and> [6] coordination ”.

Chemism

Kerimasite is the Zr analog of schorlomite and forms complex mixed crystals mainly with kimzeyite , schorlomite and andradite . The measured composition from the type locality is [X] (Ca 3.00 Mn 0.01 Ce 0.01 Nd 0.01 ) [Y] (Zr 4+ 1.72 Nb 5+ 0.14 Ti 4+ 0.08 Mg 2+ 0.02 ) [Z] (Fe 3+ 1.23 Si 0.86 Al 0.82 ).

The Al contents in the Z position are due to mixed crystal formation with Kimzeyite ( [X] Ca 3 [Y] Zr 4+ 2 [Z] (Al 3+ 2 Si) O 12 ), corresponding to the exchange reaction

  • [Z] Al 3+ = [Z] Fe 3+

At temperatures above 700 ° C there is a complete Mischbarbeit of synthetic Kimzeyit and Kerimasit. At lower temperatures, the miscibility of these components is limited and two coexisting garnets form, one rich in kimzeyite and one rich in kerimasite. This segregation was also observed in natural kerimasites from the type locality.

The Ti contents in the Y position can be added as an admixture of schorlomite [X] Ca 3 [Y] Ti 4+ 2 [Z] (Fe 3+ 2 Si) O 12 according to the exchange reaction

  • [Y] Zr 4+ + [Z] Al 3+ = [Y] Ti 4+ + [Z] Fe 3+

to be discribed. Furthermore, kerimasite forms mixed crystals with andradite [X] Ca 3 [Y] Fe 3+ 2 [Z] Si 3 O 12 according to the exchange reaction

  • [Y] Zr 4+ + [Z] Al 3+ = [Y] Fe 3+ + [Z] Si 4+

and with a hypothetical Nb 5+ analog of usturite [X] Ca 3 [Y] (Nb 5+ Zr 4+ ) [Z] Fe 3+ 3 O 12 corresponding to the exchange reaction

  • [Y] Zr 4+ + [Z] Si 4+ = [Y] Nb 5+ + [Z] Fe 3+

Kerimasite can contain up to 24% by weight of UO 3 . The compositions of natural uranium-containing kermesites follow a linear trend, that of a mixed crystal formation of kerimasite with a U 5+ analogue of usturite ( [X] Ca 3 [Y] (U 5+ Zr 4+ ) [Z] Fe 3+ 3 O 12 ) corresponds. For the natural garnets investigated so far, however, it is assumed that uranium is incorporated as U 6+ through a combination of two exchange reactions:

Installation of a U 6+ -Fe 2+ - yafsoanite component accordingly

  • [Y] Zr 4+ + 2 [Z] Fe 3+ = [Y] U 6+ + 2 [Z] Fe 2+

and mixed crystal formation with elbrusite ( [X] Ca 3 [Y] (U 6+ 0.5 R 4+ 1.5 ) [Z] Fe 3+ 3 O 12 ) accordingly

  • 0.5 [Y] Zr 4+ + [Z] Si 4+ = 0.5 [Y] U 6+ + [Z] Fe 3+

Investigations on synthetic uranium-containing grenades showed that uranium is incorporated into kermesite up to the composition of elbrusite as U 6+ . With uranium contents above 0.5 apfu, uranium is incorporated as a U 5+ analog of Usturit according to the exchange reaction

  • [Y] Zr 4+ + [Z] Si 4+ = [Y] U 5+ + [Z] Fe 3+

Crystal structure

Kerimasite crystallizes with cubic symmetry in the space group Ia 3 d (space group no. 230) with 8 formula units per unit cell . The synthetic end member has the lattice parameter a  = 12.598  Å , the natural mixed crystal from the type locality a  = 12.549 Å. Template: room group / 230

The structure is that of garnet . Calcium (Ca 2+ ) occupies the dodecahedral X positions surrounded by 8 oxygen ions, zirconium (Zr 4+ ) the octahedral Y position surrounded by 6 oxygen ions and the tetrahedral Z position surrounded by 4 oxygen ions is iron (Fe 3+ ) and silicon (Si 4+ ) occupied.

Education and Locations

Kerimasite is mainly formed in ultra-basic igneous and carbonatites at low pressure and high temperatures . Garnets rich in kerimasite have also been found in contact metamorphic skarns.

Carbonatites

The type locality of Kerimasite is a carbonatite from the Kerimasi Volcano in the Ngorongoro District , Arusha Region of Tanzania . Accompanying minerals are calcite apatite , magnesioferrite and baddelyite .

In the Polino carbonatite near Terni in Umbria , Italy , kerimasite, then still called kimzeyite, occurs in the form of 10-25 µm large, rounded crystals in fine-grained calcite together with phlogopite, perovskite, monticellite and Fe-Ti oxides.

Basic igneous rocks

The carbonate-rich areas of the lamprophyre the marathon Dikes at McKellar Harbor, Ontario , Canada lead Kerimasitreiche Melanite along with olivine, phlogopite , Andradite , calcite, perovskite, apatite and spinel, which were described at the time as yet Kimzeyit. With a few exceptions, the published analyzes are in the composition range of kerimasite.

Skarne

In the Ca-Mg- Skarn at the contact of a granodiorite with the Triassic Dolomites in the Schemnitz Mountains , Slovakia , kerimasite occurs together with andradite, monticellite, clintonite , magnetite , perovskite and brucite .

Others

In a Auswürfling from a pyroclastic flow near Anguillara Sabazia on Bracciano north of Rome in Lazio , central Italy enters Kerimasit, described at the time as yet Kimzeyit, along with gehlenite , Hercynit and pyrite on.

See also

Web links

Individual evidence

  1. ↑ a b c d e f g h i j k l m n o p q AN Zaitsev, CT Williams, SN Britvin, IV Kuznetsova, JS Pratt, SV Petrov and J. Keller: Kerimasite, Ca3Zr2 (Fe3 + 2Si) O12, a new garnet from carbonatites of Kerimasi volcano and surrounding explosion craters, northern Tanzania . In: Mineralogical Magazine . tape 74 , no. 5 , 2010, p. 803-820 ( Online [PDF; 1.8 MB ; accessed on August 26, 2017]).
  2. ↑ a b c d e f Junji Yamakawa, Chiyoko Henmi, Akira Kawahara: Syntheses and X-ray studies of Kimzeyite, Ca3Zrs (Al, Fe) 2SiO12 . In: Mineralogical Journal . tape 16 , no. 7 , 1993, pp. 371–377 ( Online [PDF; 659 kB ; accessed on August 5, 2017]).
  3. ↑ a b List of localities for kerimasite in the Mineralienatlas and Mindat
  4. ↑ Find location list for Kimzeyit in the Mineralienatlas and Mindat
  5. ↑ a b Jun Ito and Clifford Frondel: Synthetic zirconium and titanium garnets . In: American Mineralogist . tape 52 , no. 5-6 , 1967, pp. 773–781 ( Online [PDF; 545 kB ; accessed on July 8, 2017]).
  6. ^ A b Karl R. Whittle, Gregory R. Lumpkin, Frank J. Berry, Gordon Oates, Katherine L. Smith, Sergey Yudintsev, Nestor J. Zaluzec: The structure and ordering of zirconium and hafnium containing garnets studied by electron channeling, neutron diffraction and Mössbauer spectroscopy . In: Journal of Solid State Chemistry . tape 180 , 2007, p. 785-791 ( Online [PDF; 524 kB ; accessed on August 5, 2017]).
  7. ↑ FA Caporuscio, BL Scott, H. Xu, RK Feller: Garnet nuclear waste forms - Solubility at repository conditions . In: Nuclear Engineering and Design . tape 266 , 2014, p. 180–185 ( online [PDF; 1.5 MB ; accessed on July 8, 2017]).
  8. ↑ a b Xiaofeng Guo, Alexandra Navrotsky, Ravi K. Kukkadapu, Mark H. Engelhard, Antonio Lanzirotti, Matthew Newville, Eugene S. Ilton, Stephen R. Sutton, Hongwu Xu: Structure and thermodynamics of uranium-containing iron garnets . In: Geochimica et Cosmochimica Acta . tape 189 , 2016, p. 269–281 ( Online [PDF; 1.4 MB ; accessed on September 3, 2017]).
  9. ^ A b c 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 ( Online [PDF; 2,3 MB ; accessed on July 8, 2017]).
  10. ↑ a b SM Antao and LA Cruickshank: Two cubic phases in kimzeyite garnet from the type locality Magnet Cove, Arkansas . In: Acta Crystallographica Section B . tape 72 , 2016, p. 846-854 ( online [accessed August 5, 2017]).
  11. ↑ Irina O. Galuskina, Evgeny V. Galuskin, Thomas Armbruster, Biljana Lazic, Joachim Kusz, Piotr Dzierżanowski, Viktor M. Gazeev, Nikolai N. Pertsev, Krystian Prusik, Aleksandr E. Zadov, Antoni Winiarski, Roman Wrzalik, and Anatoly G Gurbanov: Elbrusite- (Zr) - A new uranium garnet from the Upper Chegem caldera, Kabardino-Balkaria, Northern Caucasus, Russia . In: American Mineralogist . tape 95 , no. 7 , 2010, p. 1172–1181 ( Online [PDF; 2.0 MB ; accessed on July 29, 2017]).
  12. ↑ L. Lupini, CT Williams, AR Woolley: Zr-rich garnet and Zr and Th-rich perovskite from the carbonatite Polino, Italy . In: Mineralogical Magazine . tape 56 , 1992, pp. 581-586 ( Online [PDF; 370 kB ; accessed on July 8, 2017]).
  13. ^ R. Grath Platt and Roger H. Mitchell: The Marathon Dikes. I: Zirconium-rich titanian garnets and manganoan magnesian ulviispinel-magnetite spinel . In: American Mineralogist . tape 64 , 1979, pp. 546-550 ( Online [PDF; 479 kB ; accessed on July 8, 2017]).
  14. ↑ UHER, PAVEL; KODERA, PETER; OZDÍN, DANIEL: Kerimasite Ca3Zr2 (Fe3 + 2Si) O12 - vzácny granát z Ca-Mg skarnovo-porfýrového ložiska Vysoká-Zlatno, štiavnický stratovulkán (stredné Slovensko). In: Bulletin Mineralogicko-Petrologickeho Oddeleni Narodniho Muzea v Praze . tape 20 , no. 1 , 2012, p. 59–62 ( online [accessed March 3, 2017]).
  15. ↑ Emanuela Schingaro, Fernando Scordari, Flavio Capitanio, Giancarlo Parodi, David C. Smith, Annibale Mottana: Crystal chemistry of kimzeyite from Anguillara, Mts. Sabatini, Italy . In: European Journal of Mineralogy . tape 13 , no. 4 , 2001, doi : 10.1127 / 0935-1221 / 2001 / 0013-0749 .