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GEOREF RECORD

Metamict aeschynite-(Y) from the Evje-Iveland district (Norway); heat-induced recrystallization and dehydrogenation

Paola Bonazzi, Matteo Zoppi and Luigi Dei
Metamict aeschynite-(Y) from the Evje-Iveland district (Norway); heat-induced recrystallization and dehydrogenation
European Journal of Mineralogy (February 2002) 14 (1): 141-150

Abstract

X-ray powder diffraction has shown that the progressive restoration of crystallinity for a metamict aeschynite starts at 350 degrees C and appears to be almost complete at 450 degrees C. During this process the water in the untreated amorphous material is released. Structural data after each successive heat treatment (450-1050 degrees C in steps of 100 degrees C) show that with the increase in T, other phases progressively crystallized (pyrochlore, rutile, brannerite). The transitions to the high-T phase (euxenite-type) occurs at approximately 1100 degrees C and appears to be more T- than time-dependent. Formula balance and structural requirements imply that some OH (super -) replaces O (super 2-) at the O4 site. The formula is given as (Y (sub 0.51) REE (sub 0.25) Th (sub 0.15) U (super 4+) (sub 0.06) Ca (sub 0.04) )(Ti (sub 1.56) Nb (sub 0.33) Ta (sub 0.05) W (sub 0.02) Fe (super 2+) (sub 0.03) )O (sub 5.52) (OH) (sub 0.48) . On heating in air at > 500 degrees C, an oxidation-dehydrogenation reaction occurs, resulting in a lengthening of the donor-acceptor distances and a related shortening of the A-O4 and B-O4 bond lengths.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 14
Serial Issue: 1
Title: Metamict aeschynite-(Y) from the Evje-Iveland district (Norway); heat-induced recrystallization and dehydrogenation
Affiliation: Universita di Firenze, Dipartimento di Scienze della Terra, Florence, Italy
Pages: 141-150
Published: 200202
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 33
Accession Number: 2002-024008
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 6 tables
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
Update Code: 200209
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