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Mineralogy of dark mica from the Wiborg rapakivi batholith, southeastern Finland

Milan Rieder, Ilmari Haapala and Pavel Povondra
Mineralogy of dark mica from the Wiborg rapakivi batholith, southeastern Finland
European Journal of Mineralogy (June 1996) 8 (3): 593-605


The chemical analyses, cell parameters, polytypes, optical and physical properties are reported for biotite from nine analysed rock samples of the main granite types of the classic Wiborg batholith. All biotite compositions plot near the annite-siderophyllite corner of the Fe (super 2+) -Mg-Li triangle for trioctahedral micas: their Fe (super 2+) /(Fe (super 2+) +Mg) ratio varies from 0.8 to 1.0, being lowest in biotites from biotite-hornblende-fayalite granites (dark wiborgite, wiborgite, tirilite) and highest in lithian siderophyllite (Li (sub 2) O 1.2-1.6 wt.%) from a topaz-bearing granite. The TiO (sub 2) content of the micas varies inversely with Fe (sub tot) /(Fe (sub tot) + Mg); it is highest in dark wiborgite (3.98 wt.%) and lowest in topaz-bearing granites (0.18%). The F is high only in lithian siderophyllite (4.2-4.9 wt.%). In the annite-phlogopite- KFe (super 3+) (sub 3 ) AlSiO (sub 12) (H (sub -1) ) diagram, all biotites plot below the magnetite-hematite oxygen buffer line; lowest fO (sub 2) is shown by annite from dark wiborgite and higher fO (sub 2) by siderophyllites from the topaz-bearing granites. It is probable that the composition of micas from the topaz granites changed by subsolidus reactions that took place during late magmatic or post-magmatic stages. In the polytypes, 1M was the most frequent, as expected, but siderophyllite from pyterlite contains polytypes 5M, 3Tc and 1M, while lithian siderophyllite ('protolithionite') from the topaz granite has 2M (sub 1) , 3T and unresolved complex structures.

ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 8
Serial Issue: 3
Title: Mineralogy of dark mica from the Wiborg rapakivi batholith, southeastern Finland
Affiliation: Charles University, Department of Geochemistry, Mineralogy and Mineral Resources, Prague, Switzerland
Pages: 593-605
Published: 199606
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 39
Accession Number: 1996-047206
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: 7 tables
N59°45'00" - N70°00'00", E19°00'00" - E31°45'00"
Secondary Affiliation: University of Helsinki, FIN, Finland
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United KingdomTwickenhamUKUnited Kingdom
Update Code: 199616
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