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High-pressure behavior of Ca/Na clinopyroxenes; the effect of divalent and trivalent 3d-transition elements

Fabrizio Nestola, Tiziana Boffa Ballaran, Ross J. Angel, Jing Zhao and Haruo Ohashi
High-pressure behavior of Ca/Na clinopyroxenes; the effect of divalent and trivalent 3d-transition elements
American Mineralogist (May 2010) 95 (5-6): 832-838

Abstract

Two C2/c pyroxenes, CaMnSi (sub 2) O (sub 6) and CaZnSi (sub 2) O (sub 6) , were investigated at high pressure by single-crystal X-ray diffraction. Their unit-cell parameters were determined at 9 different pressures up to 7.55 and 8.23 GPa, respectively. No evidence of phase transformations was found for either sample throughout the investigated pressure range. The pressure-volume data were fit using a third-order Birch-Murnaghan equation of state and it was possible to refine simultaneously the unit-cell volume V (sub 0) , the bulk modulus K (sub T0) and its first pressure derivative K' providing the following coefficients: V (sub 0) =462.01(3) Aa (super 3) , K (sub T0) =97.3(4) GPa, K'=7.5(2) for CaMnSi (sub 2) O (sub 6) and V (sub 0) =444.79(2) Aa (super 3) , K (sub T0) =109.6(5) GPa, K'=7.0(2) for CaZnSi (sub 2) O (sub 6) . The substitution of Zn for Mn at the M1 crystallographic site causes a strong decrease of the bulk modulus (by about 11%). Intensity data were collected at several pressures for both samples. The main compression mechanism is related to the tetrahedral chain kinking and the consequent shortening of the Ca-O3 (sub long) bond distances, which show a markedly larger decrease for the CaMnSi (sub 2) O (sub 6) sample. Comparing the results obtained in this work with previous data for Ca/Na-bearing C2/c pyroxenes containing trivalent and divalent 3d-transition elements at M1 site, we identified two distinct compressibility trends: for a similar unit-cell volume at room pressure the pyroxenes with Na on M2 and trivalent cations on M1 are more compressible than those having Ca on M2 and divalent cations at the M1 site. The analysis of the structure evolution for all samples indicates that this is strongly correlated with the evolution of kinking of the tetrahedral chains and the shortening of the M2-O3 bonds.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 95
Serial Issue: 5-6
Title: High-pressure behavior of Ca/Na clinopyroxenes; the effect of divalent and trivalent 3d-transition elements
Affiliation: Universita di Padova, Dipartimento di Geoscienze, Padua, Italy
Pages: 832-838
Published: 201005
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 30
Accession Number: 2010-050163
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 5 tables
Secondary Affiliation: Istituto di Geoscienze e Georisorse, ITA, ItalyUniversitaet Bayreuth, DEU, Federal Republic of GermanyVirginia Polytechnic Institute and State University, USA, United StatesHashi Institute for Silicate Science, JPN, Japan
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201027
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