Neues Mineral im kohligen Chondriten NWA 1934 (CV3) entdeckt: Brearleyite

[karmaka]

Neues Mineral im kohligen Chondriten NWA 1934 (CV3) entdeckt: Brearleyite

Researchers at Cal­tech and sev­eral author insti­tu­tions have named a newly dis­cov­ered min­eral in a mete­orite, “brear­leyite,” in recog­ni­tion of Uni­ver­sity of New Mex­ico Pro­fes­sor and Chair of Earth and Plan­e­tary Sci­ences Adrian Brear­ley for his con­tri­bu­tions to mete­orite mineralogy.

“I’m deeply hon­ored and hum­bled to say the least,” said Brear­ley. “It doesn’t hap­pen to too many people.”

Brear­leyite is an extremely rare, fine-grained min­eral that is a new mete­oritic Ca-Al (calcium-aluminum) and Cl-rich phase. The sam­ple was dis­cov­ered in a car­bona­ceous chon­drite mete­orite found in North­west Africa in 2003. It likely formed from a reac­tion of krotite with hot Cl-bearing gases or flu­ids on a small aster­oid, 4.56 bil­lion years ago. Krotite is another recently dis­cov­ered min­eral that is named after Dr. Alexan­dre Krot, a col­league and col­lab­o­ra­tor of Brearley’s at the Uni­ver­sity of Hawai’i, Manoa.

The min­eral and its name, “brear­leyite,” have been approved by the Com­mis­sion on New Min­er­als, Nomen­cla­ture and Clas­si­fi­ca­tion (CNMNC) of the Inter­na­tional Min­er­alog­i­cal Asso­ci­a­tion. Three round, thin sec­tions of one inch diam­e­ter con­tain the material.

Quelle: http://news.unm.edu/2011/08/newly-discovered-mineral-in-meteorite-named-after-unm-professor/ (29.8.2011)

Brearleyite (IMA 2010-062, Ca 12 Al 14 O 32 Cl 2 ) is a Cl-bearing mayenite, occurring as fine-grained
aggregates coexisting with hercynite, gehlenite, and perovskite in a rare krotite (CaAl 2 O 4 ) dominant
refractory inclusion from the Northwest Africa 1934 CV3 carbonaceous chondrite. The phase was
characterized by SEM, TEM-SAED, micro-Raman, and EPMA. The mean chemical composition of
the brearleyite is (wt%) Al 2 O 3  48.48, CaO 45.73, Cl 5.12, FeO 0.80, Na 2 O 0.12, TiO 2  0.03, –O 1.16,
sum 99.12. The corresponding empirical formula calculated on the basis of 34 O+Cl atoms is (Ca 11.91
Na 0.06 ) ∑11.97 (Al 13.89 Fe 0.16 Ti 0.01 ) ∑14.06 O 31.89 Cl 2.11 . The Raman spectrum of brealryeite indicates very close
structural similarity to synthetic Ca 12 Al 14 O 32 Cl 2 . Rietveld refinement of an integrated TEM-SAED
ring pattern from a FIB section quantifies this structural relationship and indicates that brearleyite
is cubic, I43d; a = 11.98(8) Å, V = 1719.1(2) Å 3 , and Z = 2. It has a framework structure in which
AlO 4  tetrahedra share corners to form eight-membered rings. Within this framework, the Cl atom is
located at a special position (3/8,0,1/4) with 0.4(2) occupancy and Ca appears to be disordered on
two partially occupied sites similar to synthetic Cl-mayenite. Brearleyite has a light olive color under
diffuse reflected light and a calculated density of 2.797 g/cm 3 . Brearleyite is not only a new meteoritic
Ca-,Al-phase, but also a new meteoritic Cl-rich phase. It likely formed by the reaction of krotite with
Cl-bearing hot gases or fluids.

Quelle: http://www.minsocam.org/msa/ammin/toc/Abstracts/2011_Abstracts/AS11_Abstracts/Ma_p1199_11.pdf

In NWA 1934 wurde bereits Krotit nachgewiesen. Hier unser thread dazu:

http://www.jgr-apolda.eu/index.php?topic=6502.0

 

Martin