Yagiit

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Yagiit
General and classification
other names

IMA 1968-020

chemical formula Na 1.5 Mg 2 (Al, Mg) 3 [(Si, Al) 12 O 30 ]
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.CM.05 ( 8th edition : VIII / E.22)
63.02.01a.10
Similar minerals Apatite , beryl , cordierite , milarite , quartz
Crystallographic Data
Crystal system hexagonal
Crystal class ; symbol 6 / mmmTemplate: crystal class / unknown crystal class
Space group P 6 / mcc (No. 192)Template: room group / 192
Lattice parameters a  = 10.09 (1)  Å ; b  = 14.20 (3) Å
Formula units Z  = 2
Physical Properties
Mohs hardness not determined
Density (g / cm 3 ) calculated: 2.9
Cleavage Please complete!
colour colorless, pale blue
Line color White
transparency translucent
shine Glass gloss
Crystal optics
Refractive indices n ω  = 1.536
n ε  = 1.544
Birefringence δ = 0.008
Optical character uniaxial positive
Pleochroism very weak:
ω = pale blue
ε = colorless

The mineral yagiite is a very rare ring silicate from the milarite group and has the chemical composition (Na 1.20 K 0.30 ) (Mg 2.00 ) (Mg 0.60 Fe 0.34 Ti 0.10 Al 1.96 ) (Si 10.22 Al 1.78 ) O 30 .

Yagiite crystallizes with hexagonal symmetry and forms colorless crystals with a glass-like sheen and can be colored pale blue due to trace amounts of iron and titanium .

Etymology and history

Yagiite was discovered in 1969 in silicate inclusions of the Colomera meteorite, a IIE-type iron meteorite found in 1912 in the province of Granada , Andalusia , Spain . Bunch and Fuchs named the new mineral from the milarite group after Dr. Kenzo Yagi, Professor of Geology at Hokkaidō University in Sapporo , Japan , in recognition of his contributions to mineralogy and petrology .

The next iron meteorite, in which not yagiite but a silicate glass with the composition of yagiite was found, hit a cargo ship loaded with cars off Tahara , Aichi-ken , Japan on April 26, 1991 . After a hit by the Dutch cargo ship "Malacca" in 1648, this was the second documented meteorite impact on a ship's deck and the first from which fragments were recovered. One of the crew members took the largest fragment home and made it available for scientific research a year and a half later.

Another mention of yagiite comes from A. Ruzicka, M. Hutson and C. Floss, who detected yagiite in the silicate inclusions of the unclassified Sombrerete iron meteorite in 2006.

classification

In the outdated, but partly still in use, 8th edition of the mineral classification according to Strunz , the yagiite belongs to the general section of " ring silicates (cyclosilicates)", where it is used together with almarudite , armenite , berezanskite , brannockite , chayesite , darapiosit , dusmatovite , eifelite , emeleusite , Faizievit , Merrihueit , Oftedalit , Osumilith , Osumilith- (Mg) , Poudretteit , Roedderite , Shibkovite , Sogdianite , Sugilite , Trattnerite and Yakovenchukit- (Y) the " Milarite-Osumilite-Group " with the system no. VIII / E.22 forms.

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 classifies the yagiit in the "ring silicates" department. 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 . With Almarudit, Armenit, Berezanskit, Brannockit, Chayesit, Darapiosit, Dusmatovit, Eifelit, Friedrichbeckeit , Klöchit , Merrihueit, Milarit, Oftedalit, Osumilith, Osumilith- (Mg), Poudretteit, Roedderit, Shibkitnerit, Sogdianit and Sogdian " Milaritgruppe " with the system no. 9.CM.05 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the yagiit to the class of "silicates and germanates", but there in the more finely divided 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

The compositions of yagiit from the two known occurrences hardly differ:

  • [C, B] (Na 1.20 K 0.30 ) [A] (Mg 2.00 ) [T2] (Mg 0.60 Fe 0.34 Ti 0.10 Al 1.96 ) [T1] (Si 10.22 Al 1.78 ) O 30 , Colomera iron meteorite
  • [C, B] (Na 0.87 K 0.39 ) [A] (Mg 1.34 Fe 2+ 0.51 Mn 0.03 Ca 0.12 ) [T2] (Mg 0.84 Al 2.16 ) [T1] (Si 10.19 Al 1.82 ) O 30 , Somberete iron meteorite

The position in the crystal structure is indicated in square brackets.

There are different statements about the idealized composition of pure yagiit. The Commission for New Minerals and Mineral Classification (CNMMN) of the IMA emphasizes the mixed occupation of the T2 position with Al and Mg and defines yagiite as the Na-Al analog of Chayesite:

  • [C] Na [A] Mg 2 [T2] (Al Mg 2 ) [Si 12 O 30 ]

In his listing of all minerals of the milarite group, Hawthorne emphasizes the agreement of the occupation of the T1 position of the 6-double-ring complex anion with osumilite (Si 10 Al 2 ) and defines yagiite as the Na analog of osumilite- (Mg) :

  • [C] Na [A] Mg 2 [T2] (Al 3 ) [Si 10 Al 2 O 30 ]

Both formulas differ significantly from the composition of the Colomera Yagiit. Its composition can be described to a good approximation as a mixture of the following end links:

  • 50% [C] Na [B] □ 2 [A] Mg 2 [T2] (Al 3 ) [Si 10 Al 2 O 30 ]: Yagiit according to Hawthorne, an Osumilith- (Na, Mg)
  • 25% [C] Na [B] □ 2 [A] Mg 2 [T2] (Al Mg 2 ) [Si 12 O 30 ]: hypothetical yagiit terminal of the IMA
  • 25% [C] Na [B] Na 2 [A] Mg 2 [T2] Mg 3 [Si 11 Al O 30 ]: synthetic end link made of glaze of a scarab

The only observed variation in the composition is an increase in the Fe content from the core to the edge of the yagiite crystals in the Somberete meteorite according to the substitution

  • [A, T2] Mg 2+ = [A, T2] Fe 2+ .

Crystal structure

Yagiite crystallizes in the structure of milarite with the space group P 6 / mcc (space group no. 192) and 2 formula units per unit cell . The lattice parameters are Template: room group / 192

  • a = 10.09 (1) Å
  • c = 14.29 (3) Å

The silicate double rings (T1 position) are occupied by 10 Si 4+ and 2 Al 3+ as in Osumilith and the T2 tetrahedron position contains Al 3+ , Mg 2+ and small amounts of other cations.

The 12-fold coordinated C position and the 9-fold coordinated B position contain the monovalent K and Na cations as well as vacancies and the octahedral A position is fully occupied by Mg 2+ .

Education and Locations

Yagiite is found in the form of tiny crystals in the base mass of alkali-rich , silicate melt inclusions in iron meteorites of type IIE. In contrast to the minerals of the milarite group Roedderit and Merrihueit, which were also discovered in meteorites, no terrestrial occurrences of yagiite are known to date.

The type locality is the Colomera meteorite, a IIE octahedrite from the province of Granada , Andalusia , Spain . Yagiit is found in alkali-rich, silicate inclusions surrounded by nickel - iron . It occurs as a finely crystalline basic mass in the spaces between titanium and aluminum-rich diopside crystals , accompanied by whitlockite , tridymite and plagioclase .

In the Somberete meteorite, also an IIE okaedrite, yagiite occurs in small crystal aggregates in silicate inclusions together with sodium-rich glass , apatite- Cl, merrillite , ilmenite , orthopyroxene and plagioclase .

The IIE iron meteorites can be divided into 5 groups according to the composition of the silicate minerals and glasses (quenched melts): from type 1 with original silicates ( olivine , pyroxene ) to type 5 with differentiated phases such as feldspar , tridymite and silicon and sodium rich glasses. Yagiite, a sodium silicate and one of the few minerals of the milarite group that hardly contains any potassium, has so far only been found in Type 5 IIE iron meteorites.

It is surprising that in such pristine rocks as iron meteorites the formation of Na-emphasized silicate melts from which minerals such as yagiite can crystallize is surprising and how this happens has not been conclusively clarified. With the previous models, such as the collision of iron meteorites with chondritic stone meteorites or fractional crystallization of chondritic melts, it is difficult to explain all the properties of the silicate inclusions. Another model explains the formation of the differently composed silicate inclusions of the IIE iron meteorites through processes during the condensation of the meteorites from the solar fog , which, depending on the temperature, could lead to different initial compositions. Subsequently, they are metasomatically changed to the wet silicate glasses observed. These are processes that only occur in meteorites, but not on earth. If this model is confirmed, it would also provide an explanation as to why yagiite has so far only been found in meteorites.

See also

literature

  • Yagiite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 69.7 kB )

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 TE Bunch, LH Fuchs (1969): Yagiite, A New Sodium-Magnesium Analogue Of Osumilite , In: American Mineralogist , 54, p. 14–18 ( PDF, 321 kB )
  2. ↑ a b c d e f g h i j k l m n o p Yagiite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 69.7 kB )
  3. ↑ Miura, Y., Haramura, H., Yanai, K., Okamoto, M., & Iancu, OG (1994): Bulk composition and classification of the Tahara meteorite which fell in Central Japan in March 1991 , In: Eighteenth Symposium on Antarctic Meteorites. Proceedings of the NIPR Symposium , 7, pp. 284–292 ( bibcode : 1994AMR ..... 7..284M )
  4. ↑ a b c d A. Ruzicka, M. Hutson, C. Floss (2006): Petrology of silicate inclusions in the Sombrerete ungrouped iron meteorite: Implications for the origins of IIE-type silicate-bearing irons , In: Meteoritics & Planetary Science , 41, pp. 1797–1831 ( PDF, 2.6 MB )
  5. ↑ a b CNMMN / CNMNC, IMA: The New IMA List of Minerals - A Work in Progress - Updated: September 2016 . September 2016 ( nrm.se [PDF]).
  6. ↑ a b 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 ( full text ).
  7. ↑ G. Artioli, I. Angelini, F. Nestola (2013): New milarite / osumilite-type phase formed during ancient glazing of an Egyptian scarab. In: Applied Physics A , Volume 110, pp. 371-377 ( doi : 10.1007 / s00339-012-7125-x )
  8. ↑ Mittlefehldt DW, McCoy TJ, Goodrich CA, and Kracher A. (1998): Non-chondritic meteorites from asteroidal bodies. , In: Planetary materials , Editor: JJ Papike, Albuquerque, New Mexico: Reviews in Mineralogy Press, 4.195, pp. 4.1 ( PDF, 47 MB )
  9. ↑ G. Kurat, E. Zinner, and ME Valera (2007): Trace element studies of silicate-rich inclusions in the Guin (UNGR) and Kodaikanal (IIE) iron meteorites , In: Meteoritics & Planetary Science , 42, p. 1441 –1463 ( PDF, 1.2 MB )