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Raman spectroscopic characteristics of Mg-Fe-Ca pyroxenes

E. Huang, C. H. Chen, T. Huang, E. H. Lin and Ji-an Xu
Raman spectroscopic characteristics of Mg-Fe-Ca pyroxenes
American Mineralogist (April 2000) 85 (3-4): 473-479


Raman spectra of several compositions of (Mg, Fe, Ca) SiO (sub 3) pyroxenes were collected at ambient conditions. More than 10 Raman vibrational modes were observed for these pyroxenes in the wavenumber range between 200 and 1200 cm (super -1) . In general, these pyroxenes are characterized by (1) the Si-O stretching modes above 800 cm (super -1) ; (2) the Si-O bending modes between 500 and 760 cm (super -1) ; (3) SiO (sub 4) rotation and metal-oxygen translation modes below 500 cm (super -1) . For a constant Ca content, frequencies of the Raman modes in the enstatite-ferrosilite (opx) and diopside-hedenbergite (cpx) series generally decrease with an increase in Fe content. This phenomenon is attributed to an increase in both the bonding lengths and the reduced mass as Fe (super 2+) is substituted for Mg. However, two modes at approximately 900 cm (super -1) in the enstatite-ferrosilite series increase in frequencies as Fe content increases. A possible explanation is to the shortening in the Si-O-Si bridging bonding bonds when the M2 sites are preferentially occupied by the iron cation. The effect of Fe substituting for Mg on the frequency shift in cpx is less profound than opx because the larger M2 was occupied by calcium and the substitution of iron and magnesium in the M1 site results in a less significant change in the bond length. The major-element composition of the (Mg,Fe,Ca)-pyroxenes, especially the orthopyroxene series, can be semi-quantitatively determined on the basis of the peak positions of their characteristic Raman modes.

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 85
Serial Issue: 3-4
Title: Raman spectroscopic characteristics of Mg-Fe-Ca pyroxenes
Affiliation: Academia Sinica, Institute of Earth sciences, Taipei, Taiwan
Pages: 473-479
Published: 200004
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 23
Accession Number: 2000-033999
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200011
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