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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2018: 2.631

CiteScore 2018: 2.55

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1945-3027
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Volume 96, Issue 8-9

Issues

Brearleyite, Ca12Al14O32Cl2, a new alteration mineral from the NWA 1934 meteorite

Chi Ma
  • Corresponding author
  • Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
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/ Harold C. Connolly Jr
  • Department of Physical Sciences, Kingsborough Community College of CUNY, Brooklyn, New York 11235, and Earth and Environmental Sciences, The Graduate Center of CUNY, New York, New York 10024, U.S.A. / Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York 10024, U.S.A. / Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, U.S.A.
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/ John R. Beckett
  • Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
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/ Oliver Tschauner
  • Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A. / High Pressure Science and Engineering Center and Department of Geoscience, University of Nevada, Las Vegas, Nevada 89154, U.S.A.
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/ George R. Rossman
  • Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
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/ Anthony R. Kampf
  • Mineral Sciences Department, Natural History Museum of Los Angeles County, Los Angeles, California 90007, U.S.A.
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/ Thomas J. Zega
  • Materials Science and Technology Division, Naval Research Laboratory, Washington, D.C. 20375, U.S.A.
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/ Stuart A. Sweeney Smith
  • Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York 10024, U.S.A. / Department of Geology, Carleton College, Northfield, Minnesota 55057, U.S.A.
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/ Devin L. Schrader
Published Online: 2015-04-02 | DOI: https://doi.org/10.2138/am.2011.3755

Abstract

Brearleyite (IMA 2010-062, Ca12Al14O32Cl2) is a Cl-bearing mayenite, occurring as fine-grained aggregates coexisting with hercynite, gehlenite, and perovskite in a rare krotite (CaAl2O4) 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%) Al2O3 48.48, CaO 45.73, Cl 5.12, FeO 0.80, Na2O 0.12, TiO2 0.03, -O 1.16, sum 99.12. The corresponding empirical formula calculated on the basis of 34 O+Cl atoms is (Ca11.91 Na0.06)Σ11.97(Al13.89Fe0.16Ti0.01)Σ14.06O31.89Cl2.11. The Raman spectrum of brealryeite indicates very close structural similarity to synthetic Ca12Al14O32Cl2. Rietveld refinement of an integrated TEM-SAED ring pattern from a FIB section quantifies this structural relationship and indicates that brearleyite is cubic, I4̅3d; a = 11.98(8) Å, V = 1719.1(2) Å3, and Z = 2. It has a framework structure in which AlO4 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/cm3. 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.

Keywords : Brearleyite; Ca12Al14O32Cl2; new mineral; Cl-bearing mayenite; NWA 1934 meteorite; CV3 carbonaceous chondrite; SAED ring pattern; Rietveld refinement

About the article

Received: 2010-12-05

Accepted: 2011-04-13

Published Online: 2015-04-02

Published in Print: 2011-08-01


Citation Information: American Mineralogist, Volume 96, Issue 8-9, Pages 1199–1206, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am.2011.3755.

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