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American Mineralogist; December 1983; v. 68; no. 11-12; p. 1113-1125
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Raman study of anorthite, calcium Tschermak's pyroxene, and gehlenite in crystalline and glassy states

Shiv K. Sharma, Bruno Simons, and H. S. Yoder

Univ. Hawaii, Hawaii Inst. Geophys., Honolulu, HI, United States
Univ. Kiel, Federal Republic of Germany
Carnegie Inst. Washington, United States

Raman spectra are reported for crystalline anorthite (An), calcium Tschermak's pyroxene (CaTs), gehlenite (Geh), and glasses of CaAl 2 Si 2 O 8 (An), CaAlAlSiO 6 (CaTs), and Ca 2 AlAlSiO 7 (Geh) composition. A small degree of Si-Al disorder in anorthite is indicated by the presence of weak Si-O-Si antisymmetric stretching modes in its spectrum. The spectrum of the glass of An composition closely resembles that of crystalline An. This correspondence indicates that the predominant species in An glass is composed of a random network of four-membered rings of TO 4 tetrahedra (where T = Si or Al). In the spectrum of glass CaTs composition the v s (T-O-T) band appears at lower frequency ( approximately 564 cm (super -1) ) than the v s (T-O-T) band of crystalline CaTs (651 cm (super -1) ). The v as (T-O-T) bands in the 900-1200 cm (super -1) region are also at lower frequencies and are relatively stronger than the v as (T-O-T) bands in the glass of An composition. The lower frequency of the v as (T-O-T) is due to an increase in Al/Si from 1 in An glass to 2 in CaTs glass. The increase in the relative intensity of the v as (T-O-T) bands is due to nonbridging oxygens. In the spectrum of glass of Geh composition the v s (T-0-T) band appears at lower frequency (552 cm (super -1) ) than in the spectrum of crystalline Geh (626 cm (super -1) ). The shift of the band toward lower frequencies in the spectrum of the glass of Geh composition indicates that most of the Al (super 3+) ions are tetrahedrally coordinated and act as network formers. A strong band at approximately 896 cm (super -1) in the spectrum of Geh glass is attributed to the presence of an appreciable amount of SiO (super 4-) 4 groups in the glass network.--Modified journal abstract.

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A. Wang, B. L. Jolliff, L. A. Haskin, K. E. Kuebler, and K. M. Viskupic
Characterization and comparison of structural and compositional features of planetary quadrilateral pyroxenes by Raman spectroscopy
American Mineralogist, July 1, 2001; 86(7-8): 790 - 806.
[Abstract] [Full Text] [PDF]


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