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Metamorphic Na- and OH-rich disordered dravite with tetrahedral boron, associated with omphacite, from Syros, Greece; chemistry and structure

Horst R. Marshall, Andreas Ertl, John M. Hughes and Catherine McCammon
Metamorphic Na- and OH-rich disordered dravite with tetrahedral boron, associated with omphacite, from Syros, Greece; chemistry and structure
European Journal of Mineralogy (October 2004) 16 (5): 817-823

Abstract

Fe-bearing dravite from a glaucophane schist from Syros, associated with omphacite, has ben characterized by EPMA, SIMS, Moessbauer spectroscopy and crystal structure determination. The optimized formula is (super X) (Na (sub 0.96) Ca (sub 0.02) [] (sub 0.02) ) (super Y) (Mg (sub 1.29) Al (sub 0.99) Fe (super 2+) (sub 0.44) Fe (super 3+) (sub 0.19) Ti (sub 0.05) [] (sub 0.04) ) (super Z) (Al (sub 4.90) Mg (sub 1.10) ) (super T) (Si (sub 5.83) B (sub 0.17) )B (sub 3) O (sub 27) [(OH) (sub 3.93) F (sub 0.07) ], with a 15.9443, c 7.2094 Aa; R 0.017. There is no significant O (super 2-) at the V and W site; the X site is almost completely filled with Na, contrary to most natural tourmalines. It is concluded that for tourmalines in the dravite-schorl series where the O1 (W) site is mainly occupied by OH (super - ) and/or F but not by O (super 2-) , an X-site occupation is favoured with Na, Mg and Al strongly disordered. This Mg-rich tourmaline is an unusual example of Al-Mg disorder which is not driven by the short-range requirements of O (super 2-) at the O1 site. Small amounts of (super [4]) B were confirmed by the chemical analysis and the relatively small T-O distance of 1.6179 Aa. The formation of this dravite (at P-T conditions of approximately 6 to 7 kbar/ approximately 400 degrees C) took place in a subduction-exhumation environment in undersaturated SiO (sub 2) -conditions.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 16
Serial Issue: 5
Title: Metamorphic Na- and OH-rich disordered dravite with tetrahedral boron, associated with omphacite, from Syros, Greece; chemistry and structure
Affiliation: Universitaet Heidelberg, Mineralogisches Institut, Heidelberg, Federal Republic of Germany
Pages: 817-823
Published: 200410
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 29
Accession Number: 2004-084042
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 5 tables
N37°25'60" - N37°25'60", E24°55'00" - E24°55'00"
Secondary Affiliation: Universitaet Wien, AUT, AustriaMiami University, USA, United StatesUniversitaet Bayreuth, DEU, Federal Republic of Germany
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United KingdomTwickenhamUKUnited Kingdom
Update Code: 200424
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