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Crystal chemistry, HRTEM analysis and polytypic behaviour of ardennite

Marco Pasero and Thomas Reinecke
Crystal chemistry, HRTEM analysis and polytypic behaviour of ardennite
European Journal of Mineralogy (October 1991) 3 (5): 819-830


Ardennite is a mixed anion silicate with ideal chemical formula (Mn,Ca,Mg) (sub 4) [(Al,Fe (super 3+) )Mg](AsO (sub 4) )(SiO (sub 4) ) (sub 2) (OH) (sub 6) . It may be regarded as a member of a polytypic family formed by two different kinds of regularly alternating layers. Ardennite, sursassite, pumpellyite and a hypothetical structure type represent the four maximum degree of order (MDO) polytypes. The results of an EPMA and HRTEM study are presented for ardennite from the Western Alps, France, and from Evvia Island (Euboea), Greece. Ardennite from Evvia has a very high Si/As ratio in the isolated [AsO (sub 4) ] tetrahedron -- <= [Si (sub 0.9) As (sub 0.104) ] -- and a considerable amount of (super vi) Mn (super 3+) . HRTEM shows the frequent occurrence of complex polytypes intergrown with the ardennite matrix, together with disordered sequences. A possible structural model for the most common complex is suggested with a doubled c period; it is characterized by a regular alternation of ardennite and the hypothetical structure. The ardennite from the Western Alps, however, shows no significant deviation from ideal stoichiometry or evidence for polytypic behaviour.

ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 3
Serial Issue: 5
Title: Crystal chemistry, HRTEM analysis and polytypic behaviour of ardennite
Affiliation: Universita di Pisa, Dipartimento di Scienze della Terra, Pisa, Italy
Pages: 819-830
Published: 199110
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 23
Accession Number: 1995-056214
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: 1 table
N42°30'00" - N51°00'00", W05°00'00" - E08°30'00"
N34°55'00" - N41°45'00", E19°30'00" - E28°45'00"
Secondary Affiliation: Ruhr-Universitaet Bochum, DEU, Federal Republic of Germany
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United KingdomTwickenhamUKUnited Kingdom
Update Code: 199520
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