« am: August 29, 2011, 18:14:31 Nachmittag »
Neues Mineral im kohligen Chondriten NWA 1934 (CV3) entdeckt: BrearleyiteResearchers 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
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