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Discovery of dmisteinbergite (hexagonal CaAl_2Si_2O_8) in the Allende meteorite: A new member of refractory silicates formed in the solar nebula

Ma, Chi and Krot, Alexander N. and Bizzarro, Martin (2013) Discovery of dmisteinbergite (hexagonal CaAl_2Si_2O_8) in the Allende meteorite: A new member of refractory silicates formed in the solar nebula. American Mineralogist, 98 (7). pp. 1368-1371. ISSN 0003-004X. doi:10.2138/am.2013.4496. https://resolver.caltech.edu/CaltechAUTHORS:20130828-160046110

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Abstract

Dmisteinbergite, CaAl_2Si_2O_8 with P6_3/mcm structure, was identified in a rounded coarse-grained igneous Type B2 Ca-,Al-rich inclusion (CAI) STP-1 from the Allende CV3 carbonaceous chondrite. STP-1 belongs to a very rare type of refractory inclusions, Fractionation and Unknown Nuclear effects (FUN) CAIs, which experienced melt evaporation and crystallization at low total gas pressure (P < 10^(−6) bar) in a high-temperature (>1200 °C) region, possibly near the proto-Sun and were subsequently radially transported away from region, possibly by a disk wind. The Allende dmisteinbergite occurs as irregular single crystals (100–600 μm in size) in contact with gehlenitic melilite and Al,Ti-diopside, poikilitically enclosing euhedral spinel, and rare anorthite. It is colorless and transparent. The mean chemical composition, determined by electron microprobe analysis, is (wt%) SiO_2 42.6, Al_2O_3 36.9, CaO 20.2, MgO 0.05, sum 99.75, giving rise to an empirical formula of Ca_(1.01)Al_(1.96)Si_(2.02)O_8. Its electron backscatter diffraction patterns are a good match to that of synthetic CaAl_2Si_2O_8 with the P6_3/mcm structure and the unit cell a = 5.10 Å, c = 14.72 Å, and Z = 2. Dmisteinbergite could have crystallized from a silicate melt at high temperature (~1200–1400 °C) via rapid cooling. Dmisteinbergite in Allende, the first find in a meteorite, is a new member of refractory silicates, among the first solid materials formed in the solar nebula.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.2138/am.2013.4496 DOIArticle
http://ammin.geoscienceworld.org/content/98/7/1368PublisherArticle
ORCID:
AuthorORCID
Ma, Chi0000-0002-1828-7033
Krot, Alexander N.0000-0002-2278-8519
Additional Information:© 2013 Mineralogical Society of America. Manuscript received February 5, 2013; Manuscript accepted April 3, 2013; Manuscript handled by Ian Swainson. SEM-EBSD was carried out at the Geological and Planetary Science Division Analytical Facility, Caltech, which is supported in part by NSF EAR-0318518 and DMR-0080065. This work was also supported by NASA grant NNX12AJ01G (A.N.K., PI). We would like to thank Andrew M. Davis, Alan Rubin, Péter Németh, an anonymous reviewer and editor Ian Swainson for helpful comments and suggestions.
Funders:
Funding AgencyGrant Number
NSFEAR-0318518
NSFDMR-0080065
NASANNX12AJ01G
Subject Keywords:Dmisteinbergite; hexagonal CaAl2Si2O8; new refractory silicate; Allende meteorite; carbonaceous chondrite; Ca-,Al-rich refractory inclusion; solar nebula; EBSD
Issue or Number:7
DOI:10.2138/am.2013.4496
Record Number:CaltechAUTHORS:20130828-160046110
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20130828-160046110
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:40984
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:30 Aug 2013 18:29
Last Modified:10 Nov 2021 04:24

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