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Muscovite- and phengite-3T; crystal structure and conditions of formation

Alessandra Amisano-Canesi, Giacomo Chiari, Giovanni Ferraris, Gabriella Ivaldi and Svetlana V. Soboleva
Muscovite- and phengite-3T; crystal structure and conditions of formation
European Journal of Mineralogy (August 1994) 6 (4): 489-496


The crystal structures of two 3T phengitic muscovites from schists in North Kazakhstan (6 << P << 9 kbar, T approximately 600 degrees C) and from the pyrope-bearing whiteschists of the Dora-Maira massif, Italy, (P approximately 30 kbar, T approximately 700 degrees C) have been refined in space group P3 (sub 1) 12. Their respective formulae and cell parameters are (K (sub 0.93) Na (sub 0.03) )(Al (sub 1.54) Fe (sub 0.25) Mg (sub 0.21) Ti (sub 0.04) )- (Si (sub 3.34) Al (sub 0.66) )O (sub 10) (OH) (sub 2) , a 5.212, c 29.804 Aa; and (K (sub 0.92) Na (sub 0.01) )- (Al (sub 1.41) Mg (sub 0.60) Ti (sub 0.02) )(Si (sub 3.54) Al (sub 0.46) )O (sub 10) (OH) (sub 2) , a 5.215, c 29.755 Aa. Although the two independent tetrahedral sites are similar in both specimens, the two independent octahedral sites appear to differ geometrically. Assuming that high P favours less distorted structures and that the presence of two independent octahedral filled sites in 3T allows for higher flexibility, the structural features of 3T micas are consistent with a greater abundance of phengite-3T in high-P metamorphic rocks. This is explained in terms of easier fitting between T and O sheets in phengite-3T compared to muscovite-3T, because of composition, and monoclinic phengite, which has only one independent filled octahedral site.

ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 6
Serial Issue: 4
Title: Muscovite- and phengite-3T; crystal structure and conditions of formation
Affiliation: Universita di Torino, Dipartimento di Scienze Mineralogiche e Petrologiche, Torino, Italy
Pages: 489-496
Published: 199408
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 34
Accession Number: 1995-001807
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: 3 tables
Secondary Affiliation: Institute of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM), RUS, Russian Federation
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United KingdomTwickenhamUKUnited Kingdom
Update Code: 199501
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