Document Type
Article
Publication Date
12-22-2023
Publication Title
Minerals
Volume
14
Issue
1
First page number:
1
Last page number:
12
Abstract
Within the Ca-Al-silicate system, dense, layered hexagonal phases occur at high temperatures and pressures between 20 and 23 GPa. They have been observed both in nature and in experiments. In this study, we describe the endmember with a dominant sixfold coordinated Si as a mineral zagamiite (IMA 2015-022a). This new mineral identified in Martian meteorites has a general formula of (Ca,Na)(Al,Fe,Mg)2(Si,Al,□)4O11, thus defining CaAl2Si3.5O11 as a previously unknown endmember of the hexagonal CAS phases. Zagamiite assumes space group P63/mmc with a unit cell of a = 5.403(2) Å, c = 12.77(3) Å, V = 322.9(11) Å3, and Z = 2. Zagamiite contains significant Fe and Mg and a substantial deficit of Na relative to plagioclase of an equivalent Al/Si, suggesting that it was formed through crystallization from a melt that was derived from a plagioclase-dominant mixture of plagioclase and clinopyroxene above the solidus beyond 20 GPa.
Keywords
Zagamiite; CaAl2Si3.5O11; CAS phase; high-pressure mineral; shock metamorphism; Martian meteorite; Zagami; NWA 856
Disciplines
Geology | Mineral Physics
File Format
File Size
3600 KB
Language
English
Rights
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Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
Repository Citation
Ma, C.,
Tschauner, O.,
Beckett, J. R.,
Greenberg, E.,
Prakapenka, V. B.
(2023).
Zagamiite, CaAl2Si3.5O11, the Hexagonal High-Pressure CAS Phase with Dominant Si, as a Mineral from Mars.
Minerals, 14(1),
1-12.
http://dx.doi.org/10.3390/min14010018