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Brearleyite, Ca12Al14O32Cl2, a new alteration mineral from the NWA 1934 meteorite
-
Chi Ma
,
Harold C. Connolly Jr
Published/Copyright:
April 2, 2015
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
Received: 2010-12-5
Accepted: 2011-4-13
Published Online: 2015-4-2
Published in Print: 2011-8-1
© 2015 by Walter de Gruyter Berlin/Boston
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Keywords for this article
Brearleyite;
Ca12Al14O32Cl2;
new mineral;
Cl-bearing mayenite;
NWA 1934 meteorite;
CV3 carbonaceous chondrite;
SAED ring pattern;
Rietveld refinement
Articles in the same Issue
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- Brearleyite, Ca12Al14O32Cl2, a new alteration mineral from the NWA 1934 meteorite
- The 3.65 Å phase in the system MgO-SiO2-H2O: Synthesis, composition, and structure
- Water in upper mantle pyroxene megacrysts and xenocrysts: A survey study
- Mesoscale twinning and crystallographic registers in biominerals
- Radiation effects on cathodoluminescence of albite
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- Elastic softening of metamict titanite CaTiSiO5: Radiation damage and annealing
- An experimental study of the diffusion of C and O in calcite in mixed CO2-H2O fluid
- Hydrochemical performance and mineralogical evolution of a dispersed alkaline substrate (DAS) remediating the highly polluted acid mine drainage in the full-scale passive treatment of Mina Esperanza (SW Spain)
- The effect of fO₂ on the partitioning and valence of V and Cr in garnet/melt pairs and the relation to terrestrial mantle V and Cr content
- An experimental study of OH solubility in rutile at 500–900 °C, 0.5–2 GPa, and a range of oxygen fugacities
- The growth interval of garnet in the UHP eclogites from the Dabie orogen, China
- Structural studies of NH4-exchanged natrolites at ambient conditions and high temperature
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