Brearleyite,
Ca12Al14O32Cl2,
a new mineral from the NWA 1934 meteorite: SAED ring pattern and
Rietveld refinement
Chi
Ma
Division
of Geological and Planetary Sciences,
California Institute of Technology, Pasadena, CA 91125
Harold C. Connolly, Jr.
Department
of Physical Sciences, Kingsborough
Community College of CUNY, Brooklyn, NY 11235 and Earth and
Environmental
Sciences, The Graduate Center of CUNY, New York, NY 10024, USA;
Department
of Earth and Planetary Sciences, American Museum of Natural History,
New York,
NY 10024, USA;
Lunar
and Planetary Laboratory, University of
Arizona, Tucson, AZ 85721, USA
John
R. Beckett, George R. Rossman
Division
of Geological and Planetary Sciences,
California Institute of Technology, Pasadena, CA 91125
Anthony
R. Kampf
Mineral
Sciences Department, Natural History
Museum of Los Angeles County, Los Angeles, CA 90007
Thomas
J. Zega
Materials
Science and Technology Division, Naval
Research Laboratory, Washington, DC 20375, USA
Oliver
Tschauner
Division
of Geological and Planetary Sciences,
California Institute of Technology, Pasadena, CA 91125
Departemnt
of Physics, University of Nevada, Las
Vegas, NV 89154, USA
Stuart
A. Sweeney
Smith
Department
of Earth and Planetary Sciences, American
Museum of Natural History, New York, NY 10024, USA
Devin
L. Schrader
Lunar
and Planetary Laboratory, University of
Arizona, Tucson, AZ 85721, USA
Department
of Geology, Carleton College,
Northfield, MN 55057, USA
Abstract
Brearleyite
(IMA
2010-062, Ca12Al14O32Cl2)
is
Cl-bearing manyenite, occurring as fine-grained aggregates along with
hercynite,
gehlenite
and
perovskite in an
uncommon krotite
(CaAl2O4)
-dominant refractory inclusion from the Northweat Africa 1934
CV3 carbonaceous
chondrite.
It is the first occurrence of Ca12Al14O32Cl2
in a meteorite, identified by FE-SEM, TEM-SAED, micro-Raman and EMPA.
It is potentially an extraterrestrial
alteration mineral. The
mean chemical composition determined by electron
microprobe analysis of this 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. Its
empirical formula
calculated on the basis of 34 O+Cl atoms is (Ca11.91Na0.06)∑11.97(Al13.89Fe0.16Ti0.01)∑14.06O31.89Cl2.11.
Rietveld
refinement of an integrated TEM-SAED ring pattern from a FIB section revealed
that brearleyite is cubic, I4bar3
d;
a =
11.9794(5) Å,
V =
1719.12(22) Å
3 and
Z = 2. It
has a framework structure in which AlO4
(aluminate) 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 0.374 occupancy and Ca
is
disordered on two partially occupied sites. It has
a dark green color and a calculated density of 2.797
g/cm3.
Brearleyite is not only a new meteoritic Ca-,
Al-phase, but also a new Cl-rich phase in a primitive meteorite
