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Complete solid solution between magnesian schorl and lithian excess-boron olenite in a pegmatite from the Koralpe (Eastern Alps, Austria)

Angelika Kalt, Werner Schreyer, Thomas Ludwig, Stefan Prowatke, Heinz-Juergen Bernhardt and Andreas Ertl
Complete solid solution between magnesian schorl and lithian excess-boron olenite in a pegmatite from the Koralpe (Eastern Alps, Austria)
European Journal of Mineralogy (December 2001) 13 (6): 1191-1205

Abstract

At the margins of a plagioclase-quartz pegmatite near Stoffhutte (Koralpe, Austroalpine realm, Austrian Alps), a new solid solution series within the tourmaline group (XY (sub 3) Z (sub 6) [T (sub 6) O (sub 18) ](BO (sub 3) ) (sub 3) V (sub 3) W) has been found, namely between magnesian schorl and lithian excess-boron olenite. At the pegmatite contact with mylonitic garnet-biotite schists, a tourmalinite band developed. Massive tourmaline cores are Mg-rich schorl with normal boron contents of 3.0 cations per formula unit that most likely formed by a reaction of melt with garnet. Within the pegmatite, only olenitic rims of increasing size, most likely formed from a fluid via the reaction plagiolase + H (sub 2) O + B (sub 2) O (sub 3) = olenite + quartz. The major compositional changes are decreasing Fe, Mg and Si contents and X (sub mg) values as well as increasing B, Al and Li contents. Over a distance of less than five centimetres, tourmaline composition determined by secondary ion microprobe (B, Li, Be, H) and electron microprobe (remaining elements, total Fe as Fe (super 2+) ) varies continuously from (Na (sub 0.90) Ca (sub 0.11) )(Fe (sub 1.61) Mg (sub 1.10) Mn (sub 0.01) Ti (sub 0.11) Zn (sub 0.01) Li (sub 0.01) Al (sub 0.10) [] (sub 0.05) ) Al (sub 6.00) [Si (sub 6.01) O (sub 18) ](B (sub 2.99) O (sub 9) )(OH (sub 3.02) F (sub 0.23) O (sub 0.75) ) to (Na (sub 0.42) Ca (sub 0.31) [] (sub 0.27) )(Fe (sub 0.14) Mg (sub 0.03) Mn (sub 0.01) Ti (sub 0.06) Li (sub 0.33) Be (sub 0.01) Al (sub 2.49) ) Al (sub 6) [Si (sub 4.91) Al (sub 0.21) B (sub 0.88) O (sub 18) ](B (sub 3.00) O (sub 9) )(OH (sub 3.38) F (sub 0.07) ). In contrast to the proton-deficient ideal olenite, the olenitic tourmaline from Stoffhutte contains 3.0-3.4 hydrogens per formula. The main substitutions are most likely (super [Y]) Al (super 3+) + (super [T]) B (super 3+) = (super [T]) Si (super 4+) + (super [Y]) (Mg, Fe) (super 2+) , which is a modified Tschermaks' substitution, (super [Y]) Al (super 3+) + (super [Y]) (Mg, Fe) (super 2+) , (super [X]) Ca (super 2+) + (super [X]) [] = 2 (super [X]) Na (super +) , (super [Y]) Al (super 3+) + (super [X]) []? = (super [X]) Na (super +) + (super [Y]) (Mg, Fe) (super 2+) and (super [Y]) Fe (super 2+) = (super [Y]) Mg (super 2+) . Coexisting muscovite and feldspar have considerable B (0.42-0.55 wt% and 71-134 ppm, respectively). Be (49-140 ppm and 79-169 ppm, respectively) and Li contents (6-9 ppm and 9-126 ppm, respectively). The apparent partition coefficient for total B between tourmaline and muscovite (D (sub B) = C (sub tur) /C (sub ms) ) varies between 6.5 and 16.8, but the values for tetrahedrally coordinated B (D (sub B(T)) range from 0 to 13.0.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 13
Serial Issue: 6
Title: Complete solid solution between magnesian schorl and lithian excess-boron olenite in a pegmatite from the Koralpe (Eastern Alps, Austria)
Affiliation: Mineralogisches Institut, Heidelberg, Federal Republic of Germany
Pages: 1191-1205
Published: 200112
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 41
Accession Number: 2002-012299
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
N46°34'60" - N47°00'00", E14°52'00" - E15°10'00"
Secondary Affiliation: Ruhr-Universitaet Bochum, DEU, Federal Republic of GermanyInstitut fuer Mineralogie und Kristallographie, AUT, Austria
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200205
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