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Germanium coordination and the germanate anomaly

Grant S. Henderson and Halan M. Wang
Germanium coordination and the germanate anomaly
European Journal of Mineralogy (August 2002) 14 (4): 733-744


The structural mechanism responsible for the germanate anomaly along the X (sub 2) O-GeO (sub 2) join, where X = Li, Na, K, Rb, and Cs, was investigated using Raman spectroscopy. Density maxima were measured at approximately 17.5-20 mol%, 15 mol%, and 10 mol% for Li (sub 2) O, Na (sub 2) O and K (sub 2) O, respectively. A maximum at 15 mol% and a minimum at 32.5 mol% were measured for Rb (sub 2) O while the Cs (sub 2) O glasses exhibited a maximum at 17.5 mol%. A coordination change of (super IV) Ge to (super VI) Ge was not observed. It is proposed that the germanate anomaly is a consequence of formation of small 3-membered GeO (sub 4) rings as alkali oxide is added to the glass. The small rings cause a density increase. The anomaly maximum is reached when continued small ring formation cannot occur without straining the glass network. At this point the network generates large numbers of Q (super 3) non-bridging oxygens (NBOs) and at higher alkali oxide contents, Q (super 2) NBOs. The formation of the NBOs causes a decline in the density. The Rb (sub 2) O- and Cs (sub 2) O-containing glasses do not exhibit similar density trends to the lighter alkali-containing glasses. This is because of competing density effects from small-ring formation and the increased mass of the alkalis. The overall effect on the density trends of these glasses is to skew the anomaly maxima to higher alkali oxide compositions.

ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 14
Serial Issue: 4
Title: Germanium coordination and the germanate anomaly
Affiliation: University of Toronto, Department of Geology, Toronto, ON, Canada
Pages: 733-744
Published: 200208
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 69
Accession Number: 2002-064884
Categories: Geochemistry of rocks, soils, and sedimentsIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200220
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