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Virtually pure ottrelite from the region of Ottre, Belgium

Thomas Theye and Andre-Mathieu Fransolet
Virtually pure ottrelite from the region of Ottre, Belgium
European Journal of Mineralogy (August 1994) 6 (4): 547-555


Very Mn-rich chloritoid with a composition near the ottrelite end-member, Mn (super 2+) (sub 2 ) Al (sub 4) O (sub 2) [SiO (sub 4) ] (sub 2) (OH) (sub 4) , has been found for the first time, near the type locality Ottre in the Venn-Stavelot massif. The ottrelite occurs as minute inclusions in andalusite in metapelites that were metamorphosed at approximately 400 degrees C. The compositional spread of this ottrelite ranges from Mn (super 2+) (sub 96 ) Fe (super 2+) (sub 3 ) Mg (sub 1) to Mn (super 2+) (sub 65 ) Fe (super 2+) (sub 4 ) Mg (sub 31) (mol.% of divalent cations). Associated minerals are hematite, quartz, spessartine, manganian andalusite (1-12 mol.% kanonaite), muscovite, paragonite, gahnite and ardennite. Microstructural relationships are interpreted to indicate that the present mineral paragenesis with andalusite and spessartine was preceded by a paragenesis of ottrelite without garnet and andalusite, implying the disappearance of ottrelite according to the reaction ottrelite + quartz = andalusite + spessartine + H (sub 2) O; thermodynamic calculations suggest that this reaction occurs at approximately 350 degrees C (at 2 kbar). With increasing T, chloritoid in the Mn-Mg system rapidly becomes enriched in Mg within a small T interval (X (sub Mg) approximately 0 to 0.4 within 20 degrees C). Because of slow reaction rates at low T, chemical equilibrium was not attained, accounting for the compositional spread of this ottrelite.

ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 6
Serial Issue: 4
Title: Virtually pure ottrelite from the region of Ottre, Belgium
Affiliation: Technische Universitat Braunschweig, Institut fur Geowissenschaften, Brunswick, Federal Republic of Germany
Pages: 547-555
Published: 199408
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 33
Accession Number: 1995-001812
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
N49°30'00" - N50°30'00", E04°10'00" - E05°30'00"
N49°30'00" - N51°30'00", E02°30'00" - E06°30'00"
Secondary Affiliation: Universite de Liege, BEL, Belgium
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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