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Krotite, CaAl_2O_4, a new refractory mineral from the NWA 1934 meteorite

Ma, Chi and Kampf, Anthony R. and Connolly, Harold C., Jr. and Beckett, John R. and Rossman, George R. and Sweeney Smith, Stuart A. and Schrader, Devin L. (2011) Krotite, CaAl_2O_4, a new refractory mineral from the NWA 1934 meteorite. American Mineralogist, 96 (5-6). pp. 709-715. ISSN 0003-004X.

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Krotite, CaAl_2O_4, occurs as the dominant phase in an unusual Ca-,Al-rich refractory inclusion from the NWA 1934 CV3 carbonaceous chondrite. Krotite occupies the central and mantle portions of the inclusion along with minor perovskite, gehlenite, hercynite, and Cl-bearing mayenite, and trace hexamolybdenum. A layered rim surrounds the krotite-bearing regions, consisting from inside to outside of grossite, mixed hibonite, and spinel, then gehlenite with an outermost layer composed of Al-rich diopside. Krotite was identified by XRD, SEM-EBSD, micro-Raman, and electron microprobe. The mean chemical composition determined by electron microprobe analysis of krotite is (wt%) Al_2O_3 63.50, CaO 35.73, sum 99.23, with an empirical formula calculated on the basis of 4 O atoms of Ca_(1.02)Al_(1.99)O_4. Single-crystal XRD reveals that krotite is monoclinic, P2_1/n; a = 8.6996(3), b = 8.0994(3), c = 15.217(1) Å, β = 90.188(6), and Z = 12. It has a stuffed tridymite structure, which was refined from single-crystal data to R_1 = 0.0161 for 1014 F_o > 4σF reflections. Krotite is colorless and transparent with a vitreous luster and white streak. Mohs hardness is ~6½. The mineral is brittle, with a conchoidal fracture. The calculated density is 2.94 g/cm3. Krotite is biaxial (–), α = 1.608(2), β = 1.629(2), γ = 1.635(2) (white light), 2V_(meas) = 54.4(5)°, and 2V_(calc) = 55.6°. No dispersion was observed. The optical orientation is X = b; Y ≈ a; Z ≈ c. Pleochroism is colorless to very pale gray, X > Y = Z. Krotite is a low-pressure CaAl_2O_4 mineral, likely formed by condensation or crystallization from a melt in the solar nebula. This is the first reported occurrence of krotite in nature and it is one of the earliest minerals formed in the solar system.

Item Type:Article
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URLURL TypeDescription
Ma, Chi0000-0002-1828-7033
Kampf, Anthony R.0000-0001-8084-2563
Rossman, George R.0000-0002-4571-6884
Additional Information:© 2011 Mineralogical Society of America. Manuscript received September 14, 2010. Manuscript accepted January 29, 2011. Manuscript handled by Andrew McDonald. SEM, EBSD, and electron microprobe analyses were carried out at the Caltech GPS Division Analytical Facility, which is supported, in part, by grant NSF EAR- 0318518 and the MRSEC Program of the NSF under DMR-0080065. XRD studies were carried out with support from the John Jago Trelawney Endowment to the Mineral Sciences Department of the Natural History Museum of Los Angeles County. This research was also supported by NSF REU grant no. AST 0851362 and NASA OSS grants no. NNX09AB86G (H.C. Connolly Jr.), and NNX09AG40G (E.M. Stolper). We thank Andrew McDonald, Makoto Kimura, and Takashi Mikouchi for constructive reviews of this manuscript.
Funding AgencyGrant Number
John Jago Trelawney EndowmentUNSPECIFIED
NSF REUAST 0851362
Subject Keywords:Krotite, CaAl_2O_4, new mineral, refractory inclusion, NWA 1934 meteorite, CV3 carbonaceous chondrite, XRD, EBSD
Issue or Number:5-6
Record Number:CaltechAUTHORS:20110608-074522821
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Official Citation:Krotite, CaAl2O4, a new refractory mineral from the NWA 1934 meteorite Chi Ma, Anthony R. Kampf, Harold C. Connolly Jr., John R. Beckett, George R. Rossman, Stuart A. Sweeney Smith, and Devin L. Schrader
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:23938
Deposited By: Ruth Sustaita
Deposited On:08 Jun 2011 15:25
Last Modified:09 Mar 2020 13:19

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