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

Chi Ma, Harold C. Connolly, John R. Beckett, Oliver Tschauner, George R. Rossman, Anthony R. Kampf, Thomas J. Zega, Stuart A. Sweeney Smith, Devin L. Schrader

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21 Scopus citations


Brearleyite (IMA 2010-062, Ca12Al14O 32Cl2) 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, -2O 1.16 2, ∑ 99.12. The corresponding empirical formula calculated on the basis of 34 O+Cl atoms is (Ca11.91 Na0.06)?11.97(Al13.89Fe 0.16Ti0.01)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, I43d; 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.

Original languageEnglish (US)
Pages (from-to)1199-1206
Number of pages8
JournalAmerican Mineralogist
Issue number8-9
StatePublished - 2011
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology


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