Skip to Main Content
GEOREF RECORD

The johannsenite-hedenbergite complete solid solution; clinopyroxenes from the Campiglia Marittima skarn

Gian Carlo Capitani and Marcello Mellini
The johannsenite-hedenbergite complete solid solution; clinopyroxenes from the Campiglia Marittima skarn
European Journal of Mineralogy (December 2000) 12 (6): 1215-1227

Abstract

Clinopyroxenes from the Campiglia Marittima skarn range from hedenbergite to johannsenite (Jh (sub 7) to Jh (sub 100) ). Twenty single-crystals were selected for structural refinements and electron microprobe analyses. (100) twins were present and treated using a halved data set. End-member johannsenite is best approximated by the crystal Jh7GJ2, with a formula Na (sub 0.01) Ca (sub 0.96) Mn (sub 0.99) Mg (sub 0.02) Fe (sub 0.01) Al (sub 0.01) Si (sub 2.00) O (sub 6) , which was refined to R (sub obs) = 0.024. The structural change along the johannsenite-hedenbergite join is interpreted using the concept of the I-beam module. For instance, the variation of lattice parameters with composition is markedly anisotropic, being minimal along c (the I-beam direction), intermediate along a (perpendicular to the bases of adjacent I-beams) and maximal along b (parallel to the base of the I-beam). The replacement of manganese for iron expands and deforms the M1 polyhedron, and determines further coupling effects in the M2 and T polyhedra. These effects mostly consist of a more deformed M2 geometry, with longer M2-O bonds, and larger differences between the bridging and non-bridging T-O bond distances. Both the compositional and structural data indicate a complete solid solution between johannsenite and hedenbergite. All the different crystal structure parameters (lattice constants, bond distances, distortion parameters) vary continuously. Their trends suggest small values for the thermodynamic excess functions, implying limited deviations from the ideal solid solution along the johannsenite-hedenbergite join.


ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 12
Serial Issue: 6
Title: The johannsenite-hedenbergite complete solid solution; clinopyroxenes from the Campiglia Marittima skarn
Affiliation: Universite des Sciences et Technologie de Lille, Villeneuve d'Ascq, France
Pages: 1215-1227
Published: 200012
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 30
Accession Number: 2001-040134
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
N36°30'00" - N47°30'00", E06°30'00" - E19°00'00"
Secondary Affiliation: Universita di Siena, ITA, Italy
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200112
Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal