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Chiavennite revisited; a high-temperature in situ single-crystal X-ray diffraction study

Georgia Cametti and Thomas Armbruster
Chiavennite revisited; a high-temperature in situ single-crystal X-ray diffraction study
European Journal of Mineralogy (June 2015) 27 (5): 659-667


Chiavennite (CaMnBeSi (sub 5) O (sub 13) (OH) (sub 2) . 2H (sub 2) O, Z = 4) is a rare Be-bearing zeolite mineral with an interrupted framework of four-connected [SiO (sub 4) ] and three-connected [BeO (sub 4) ] tetrahedra. A sample from the type locality in the Rhetic Alps of Italy has been re-investigated at room temperature in order to clarify the space-group ambiguity discussed in the literature and to explore the system of hydrogen bonds. In addition, the thermal stability of this zeolite was tracked by in situ single-crystal X-ray diffraction between 25 degrees C and 425 degrees C. In spite of the pseudo-orthorhombic cell dimension, the new data indicate that at room temperature chiavennite is truly monoclinic P2 (sub 1) /c (beta approximately 90 degrees ) and twinned as recently shown for the new mineral ferrochiavennite. The dehydration experiments under dry conditions at different temperatures showed that chiavennite continuously released water up to at least 425 degrees C without topological modification. The loss of more than one H (sub 2) O molecule at 250 degrees C decreases the Ca coordination from eight- to seven-fold. After release of the first H (sub 2) O molecule, and strong dynamic disorder of the remaining H (sub 2) O, chiavennite evolves into orthorhombic symmetry of space group Pbcn. The continuous monoclinic-orthorhombic transition from space group P2 (sub 1) /c to Pbcn upon dehydration is attributed to loosening of the system of hydrogen bonds with extraframework H (sub 2) O as donor and oxygen at the cavity walls as acceptor.

ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 27
Serial Issue: 5
Title: Chiavennite revisited; a high-temperature in situ single-crystal X-ray diffraction study
Affiliation: University of Bern, Institute of Geological Sciences, Bern, Switzerland
Pages: 659-667
Published: 20150629
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 17
Accession Number: 2015-082106
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables
N46°19'00" - N46°19'00", E09°24'00" - E09°24'00"
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2022, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201535
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