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Incorporation of Mg in phase Egg, AlSiO (sub 3) OH; toward a new polymorph of phase H, MgSiH (sub 2) O (sub 4) , a carrier of water in the deep mantle

Luca Bindi, Aleksandra Bendeliani, Andrey Bobrov, Ekaterina Matrosova and Tetsuo Irifune
Incorporation of Mg in phase Egg, AlSiO (sub 3) OH; toward a new polymorph of phase H, MgSiH (sub 2) O (sub 4) , a carrier of water in the deep mantle
American Mineralogist (January 2020) 105 (1): 132-135

Abstract

The crystal structure and chemical composition of a crystal of Mg-bearing phase Egg with a general formula M (sub 1-x) (super 3+) M (sub x) (super 2+) SiO (sub 4) H (sub 1+x) (M (super 3+) =Al, Cr; M (super 2+) =Mg, Fe), where x=35, produced by subsolidus reaction at 24 GPa and 1400 degrees C of components of subducted oceanic slabs (peridotite, basalt, and sediment), was analyzed by electron microprobe and single-crystal X-ray diffraction. Neglecting the enlarged unit cell and the consequent expansion of the coordination polyhedra (as expected for Mg substitution for Al), the compound was found to be topologically identical to phase Egg, AlSiO (sub 3) OH, space group P2 (sub 1) /n, with lattice parameters a=7.2681(8), b=4.3723(5), c=7.1229(7) Aa, beta =99.123(8) degrees , V=223.49(4) Aa (super 3) , and Z=4. Bond-valence considerations lead to hypothesize the presence of hydroxyl groups only, thereby excluding the presence of the molecular water that would be present in the hypothetical end-member MgSiO (sub 3) .H (sub 2) O. We thus demonstrate that phase Egg, considered as one of the main players in the water cycle of the mantle, can incorporate large amounts of Mg in its structure and that there exists a solid solution with a new hypothetical MgSiH (sub 2) O (sub 4) end-member, according to the substitution Al (super 3+) <-->Mg (super 2+) +H (super +) . The new hypothetical MgSiH (sub 2) O (sub 4) end-member would be a polymorph of phase H, a leading candidate for delivering significant water into the deepest part of the lower mantle.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 105
Serial Issue: 1
Title: Incorporation of Mg in phase Egg, AlSiO (sub 3) OH; toward a new polymorph of phase H, MgSiH (sub 2) O (sub 4) , a carrier of water in the deep mantle
Affiliation: Universita di Firenze, Dipartimento di Scienze della Terra, Florence, Italy
Pages: 132-135
Published: 202001
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 31
Accession Number: 2020-006865
Categories: Geophysics of minerals and rocksSolid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
Secondary Affiliation: CNR, Istituto di Geoscienze e Georisorse, ITA, ItalyMoscow State University, RUS, Russian FederationRussian Academy of Sciences, Vernadsky Institute of Geochemistry and Analytical Chemistry, RUS, Russian FederationRussian Academy of Sciences, Institute of Experimental Mineralogy, RUS, Russian FederationEhime University, JPN, JapanTokyo Institute of Technology, JPN, Japan
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202006
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